<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e471f-06db-7aa5-98ab-f84bfbb1218d,g:500dd757-d665-4be5-8a2f-61a495e53f7f-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.ngsgi.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="simple" xlink:href="ngs-20260630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e471f-07b2-76b9-a1b0-d989185bab69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_StatementTable_019e471f-07b2-76b9-a1b0-d989185bab69" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019e471f-07b2-7cf5-903a-3bb3c2dc1dbd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e471f-07b2-76b9-a1b0-d989185bab69" xlink:to="loc_srt_ProductOrServiceAxis_019e471f-07b2-7cf5-903a-3bb3c2dc1dbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e471f-07b2-7cf5-903a-3bb3c2dc1dbd_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019e471f-07b2-7cf5-903a-3bb3c2dc1dbd" xlink:to="loc_srt_ProductsAndServicesDomain_019e471f-07b2-7cf5-903a-3bb3c2dc1dbd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e471f-07b2-79d7-b592-d05c86d26844" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019e471f-07b2-7cf5-903a-3bb3c2dc1dbd" xlink:to="loc_srt_ProductsAndServicesDomain_019e471f-07b2-79d7-b592-d05c86d26844" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_ProductSalesMember_019e471f-07b2-73ce-a9e3-9213851f5c41" xlink:href="ngs-20260630.xsd#ngs_ProductSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e471f-07b2-79d7-b592-d05c86d26844" xlink:to="loc_ngs_ProductSalesMember_019e471f-07b2-73ce-a9e3-9213851f5c41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_AftermarketServicesMember_019e471f-07b2-734a-9752-3f5e15058f25" xlink:href="ngs-20260630.xsd#ngs_AftermarketServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e471f-07b2-79d7-b592-d05c86d26844" xlink:to="loc_ngs_AftermarketServicesMember_019e471f-07b2-734a-9752-3f5e15058f25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_019e471f-07b2-7c00-bdce-128cc3a514e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_RevenuesAbstract_019e471f-07b2-7c00-bdce-128cc3a514e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RentalIncomeNonoperating_019e471f-07b2-7dad-8bbe-25c36128173f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RentalIncomeNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019e471f-07b2-7c00-bdce-128cc3a514e2" xlink:to="loc_us-gaap_RentalIncomeNonoperating_019e471f-07b2-7dad-8bbe-25c36128173f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e471f-07b2-7c36-975e-213aba4b379e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019e471f-07b2-7c00-bdce-128cc3a514e2" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e471f-07b2-7c36-975e-213aba4b379e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019e471f-07b2-70e9-9bd7-819c29293c5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019e471f-07b2-7c00-bdce-128cc3a514e2" xlink:to="loc_us-gaap_Revenues_019e471f-07b2-70e9-9bd7-819c29293c5c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_019e471f-07b2-7bd2-b936-13fed071f5eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_019e471f-07b2-7bd2-b936-13fed071f5eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DirectCostsOfLeasedAndRentedPropertyOrEquipment_019e471f-07b2-73b8-86e0-ef82518b77c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DirectCostsOfLeasedAndRentedPropertyOrEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019e471f-07b2-7bd2-b936-13fed071f5eb" xlink:to="loc_us-gaap_DirectCostsOfLeasedAndRentedPropertyOrEquipment_019e471f-07b2-73b8-86e0-ef82518b77c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostOfOperatingRevenue_019e471f-07b2-7ca4-a4e9-8d1664079d41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCostOfOperatingRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019e471f-07b2-7bd2-b936-13fed071f5eb" xlink:to="loc_us-gaap_OtherCostOfOperatingRevenue_019e471f-07b2-7ca4-a4e9-8d1664079d41" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfPropertyRepairsAndMaintenance_019e471f-07b2-7c3c-8323-1d779d5049da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfPropertyRepairsAndMaintenance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019e471f-07b2-7bd2-b936-13fed071f5eb" xlink:to="loc_us-gaap_CostOfPropertyRepairsAndMaintenance_019e471f-07b2-7c3c-8323-1d779d5049da" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_019e471f-07b2-70ef-814b-177b9df73dbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019e471f-07b2-7bd2-b936-13fed071f5eb" xlink:to="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_019e471f-07b2-70ef-814b-177b9df73dbf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019e471f-07b2-7e99-9bb1-37c539866f2f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019e471f-07b2-7e99-9bb1-37c539866f2f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019e471f-07b2-7f10-b927-28ace5bfda4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019e471f-07b2-7f10-b927-28ace5bfda4e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_InventoryAllowance_019e471f-07b2-7192-a4d7-8e9a2d54e3de" xlink:href="ngs-20260630.xsd#ngs_InventoryAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_ngs_InventoryAllowance_019e471f-07b2-7192-a4d7-8e9a2d54e3de" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_019e471f-07b2-7d11-ab54-2f305329c18a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_019e471f-07b2-7d11-ab54-2f305329c18a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfPropertyPlantEquipment_019e471f-07b2-77d1-b214-8f2b75251ccc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_GainLossOnSaleOfPropertyPlantEquipment_019e471f-07b2-77d1-b214-8f2b75251ccc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019e471f-07b2-7209-9521-e8786e763b68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_CostsAndExpenses_019e471f-07b2-7209-9521-e8786e763b68" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019e471f-07b2-7e6b-97d3-fadef4d1d095" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_OperatingIncomeLoss_019e471f-07b2-7e6b-97d3-fadef4d1d095" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e471f-07b2-7a38-93db-717b7245f752" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e471f-07b2-7a38-93db-717b7245f752" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019e471f-07b2-782a-b637-64fa8bf5fc67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e471f-07b2-7a38-93db-717b7245f752" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019e471f-07b2-782a-b637-64fa8bf5fc67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_019eb65f-3edc-79c8-b4b5-37701599103f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e471f-07b2-7a38-93db-717b7245f752" xlink:to="loc_us-gaap_InvestmentIncomeInterest_019eb65f-3edc-79c8-b4b5-37701599103f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019e471f-07b2-7a61-aea8-55acc7f714b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e471f-07b2-7a38-93db-717b7245f752" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019e471f-07b2-7a61-aea8-55acc7f714b3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019e471f-07b2-73f1-a25f-eac77f43c3fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019e471f-07b2-7a38-93db-717b7245f752" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019e471f-07b2-73f1-a25f-eac77f43c3fb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e471f-07b2-7e8a-895f-b795d0da1483" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019e471f-07b2-7e8a-895f-b795d0da1483" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019e471f-07b2-7aa2-8e4c-88e7d8d79721" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019e471f-07b2-7aa2-8e4c-88e7d8d79721" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e471f-07b2-72c4-aa4f-289ea800be4b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_NetIncomeLoss_019e471f-07b2-72c4-aa4f-289ea800be4b" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_019e471f-07b2-7198-a121-3e04b1adaa02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_us-gaap_EarningsPerShareAbstract_019e471f-07b2-7198-a121-3e04b1adaa02" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019e471f-07b2-7359-81c6-4386e62f3285" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_019e471f-07b2-7198-a121-3e04b1adaa02" xlink:to="loc_us-gaap_EarningsPerShareBasic_019e471f-07b2-7359-81c6-4386e62f3285" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019e471f-07b2-7b1a-a52a-34033cd78204" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_019e471f-07b2-7198-a121-3e04b1adaa02" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019e471f-07b2-7b1a-a52a-34033cd78204" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_WeightedAverageSharesOutstandingBasicAndDilutedAbstract_019e471f-07b2-75f4-9f93-d640ddbc4f8f" xlink:href="ngs-20260630.xsd#ngs_WeightedAverageSharesOutstandingBasicAndDilutedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-746e-9950-61e7f72fa74a" xlink:to="loc_ngs_WeightedAverageSharesOutstandingBasicAndDilutedAbstract_019e471f-07b2-75f4-9f93-d640ddbc4f8f" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019e471f-07b2-7ac8-9c51-f897c4349565" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ngs_WeightedAverageSharesOutstandingBasicAndDilutedAbstract_019e471f-07b2-75f4-9f93-d640ddbc4f8f" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019e471f-07b2-7ac8-9c51-f897c4349565" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019e471f-07b2-74d0-881d-c787d219ba14" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ngs_WeightedAverageSharesOutstandingBasicAndDilutedAbstract_019e471f-07b2-75f4-9f93-d640ddbc4f8f" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019e471f-07b2-74d0-881d-c787d219ba14" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="ngs-20260630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019e471f-07b2-7b64-a617-71b821ffe459" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019e471f-07b2-7503-ba15-a2d2d9557188" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-7b64-a617-71b821ffe459" xlink:to="loc_us-gaap_StatementTable_019e471f-07b2-7503-ba15-a2d2d9557188" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e471f-07b2-7f45-8f96-94b587ce85b9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019e471f-07b2-7503-ba15-a2d2d9557188" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e471f-07b2-7f45-8f96-94b587ce85b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e471f-07b2-7f45-8f96-94b587ce85b9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e471f-07b2-7f45-8f96-94b587ce85b9" xlink:to="loc_us-gaap_EquityComponentDomain_019e471f-07b2-7f45-8f96-94b587ce85b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e471f-07b2-7151-9e74-023a9ea8e0a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e471f-07b2-7f45-8f96-94b587ce85b9" xlink:to="loc_us-gaap_EquityComponentDomain_019e471f-07b2-7151-9e74-023a9ea8e0a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_019e471f-07b2-71c7-8ec3-82c87bb551ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e471f-07b2-7151-9e74-023a9ea8e0a6" xlink:to="loc_us-gaap_PreferredStockMember_019e471f-07b2-71c7-8ec3-82c87bb551ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e471f-07b2-76f7-8585-6b2c747449b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e471f-07b2-7151-9e74-023a9ea8e0a6" xlink:to="loc_us-gaap_CommonStockMember_019e471f-07b2-76f7-8585-6b2c747449b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019e471f-07b2-7894-8b43-b601b17b4080" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e471f-07b2-7151-9e74-023a9ea8e0a6" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019e471f-07b2-7894-8b43-b601b17b4080" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019e471f-07b2-7164-ac81-29783fe1fced" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e471f-07b2-7151-9e74-023a9ea8e0a6" xlink:to="loc_us-gaap_RetainedEarningsMember_019e471f-07b2-7164-ac81-29783fe1fced" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019e471f-07b2-7bde-84f0-1526cd8a3047" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e471f-07b2-7151-9e74-023a9ea8e0a6" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019e471f-07b2-7bde-84f0-1526cd8a3047" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019e471f-07b2-7b64-a617-71b821ffe459" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_019e471f-07b2-71b0-8dbb-6fba815994b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_PreferredStockSharesIssued_019e471f-07b2-71b0-8dbb-6fba815994b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e471f-07b2-7a81-983f-08ad4c9ac16f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_StockholdersEquity_019e471f-07b2-7a81-983f-08ad4c9ac16f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019e471f-07b2-7378-aebe-0bd7732f9f65" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_CommonStockSharesIssued_019e471f-07b2-7378-aebe-0bd7732f9f65" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019e471f-07b2-708a-ad97-cf479b5a307b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_TreasuryStockCommonShares_019e471f-07b2-708a-ad97-cf479b5a307b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_APICShareBasedPaymentArrangementIncreaseForCostRecognitionIncludingCommonStock_019e471f-07b2-7d75-bfc7-08768313fe7a" xlink:href="ngs-20260630.xsd#ngs_APICShareBasedPaymentArrangementIncreaseForCostRecognitionIncludingCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_ngs_APICShareBasedPaymentArrangementIncreaseForCostRecognitionIncludingCommonStock_019e471f-07b2-7d75-bfc7-08768313fe7a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019e471f-07b2-75f5-8975-f415bcc95217" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019e471f-07b2-75f5-8975-f415bcc95217" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_019e471f-07b2-72d5-99a8-63d78d3f6ad8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_019e471f-07b2-72d5-99a8-63d78d3f6ad8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019e471f-07b2-7838-92ff-5f359c9aadf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019e471f-07b2-7838-92ff-5f359c9aadf3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019e471f-07b2-7f87-b1b6-f6952abf21b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019e471f-07b2-7f87-b1b6-f6952abf21b6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_019e471f-07b2-754d-a16a-b1b6c3e9a324" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_019e471f-07b2-754d-a16a-b1b6c3e9a324" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_019e471f-07b2-71b4-92f5-efdb5fb3a7f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_019e471f-07b2-71b4-92f5-efdb5fb3a7f0" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_019f3da2-cca3-74d1-9287-157c81a66415" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_019f3da2-cca3-74d1-9287-157c81a66415" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_019f3da1-2afe-7ada-a883-63be91013ecc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_019f3da1-2afe-7ada-a883-63be91013ecc" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStock_019e471f-07b2-7821-938b-51983e8f7b13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_DividendsCommonStock_019e471f-07b2-7821-938b-51983e8f7b13" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019e471f-07b2-75d0-96df-7d138385dfad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019e471f-07b2-7d9a-adaf-f6c3f1c13d33" xlink:to="loc_us-gaap_NetIncomeLoss_019e471f-07b2-75d0-96df-7d138385dfad" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_019e471f-07b2-780a-9475-ea45a07026d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019e471f-07b2-7a9a-8dfd-2130e3459b28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019e471f-07b2-7575-a8bb-fe3a4e1a8805" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019e471f-07b2-739c-8ab1-0bb80f49d0d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonShares"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/BusinessCombinationNarrativeDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#BusinessCombinationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/BusinessCombinationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019fb855-f6a8-71ba-8ca9-d1479341dd96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fb855-f6a8-7165-87ae-11c15f0cfc0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb855-f6a8-71ba-8ca9-d1479341dd96" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fb855-f6a8-7165-87ae-11c15f0cfc0f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fcb48-fc5f-78fb-a275-da68b8d4f51d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fb855-f6a8-7165-87ae-11c15f0cfc0f" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fcb48-fc5f-78fb-a275-da68b8d4f51d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcb48-fc5f-78fb-a275-da68b8d4f51d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fcb48-fc5f-78fb-a275-da68b8d4f51d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcb48-fc5f-78fb-a275-da68b8d4f51d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcb48-fc5f-76f0-8f08-51a249111153" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fcb48-fc5f-78fb-a275-da68b8d4f51d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcb48-fc5f-76f0-8f08-51a249111153" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_FlatrockAcquisitionMember_019fcb81-08af-7702-aa0c-f161812397c7" xlink:href="ngs-20260630.xsd#ngs_FlatrockAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcb48-fc5f-76f0-8f08-51a249111153" xlink:to="loc_ngs_FlatrockAcquisitionMember_019fcb81-08af-7702-aa0c-f161812397c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd0c2-fb80-77b4-a713-2ce805a73567" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fb855-f6a8-7165-87ae-11c15f0cfc0f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd0c2-fb80-77b4-a713-2ce805a73567" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd0c2-fb80-77b4-a713-2ce805a73567_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd0c2-fb80-77b4-a713-2ce805a73567" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd0c2-fb80-77b4-a713-2ce805a73567_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd0c2-fb80-7c13-bbf7-35faa7ea3506" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019fd0c2-fb80-77b4-a713-2ce805a73567" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd0c2-fb80-7c13-bbf7-35faa7ea3506" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_019fd6ad-4a5c-7a55-ba67-aad0489dee5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd0c2-fb80-7c13-bbf7-35faa7ea3506" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_019fd6ad-4a5c-7a55-ba67-aad0489dee5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_019fd0c4-b5f3-7dfc-a701-1d55b6c5e7a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019fd0c2-fb80-7c13-bbf7-35faa7ea3506" xlink:to="loc_us-gaap_TradeNamesMember_019fd0c4-b5f3-7dfc-a701-1d55b6c5e7a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_PowerOfRentedFleetAcquired_019fcb81-08af-7916-921b-453e704b2726" xlink:href="ngs-20260630.xsd#ngs_PowerOfRentedFleetAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb855-f6a8-71ba-8ca9-d1479341dd96" xlink:to="loc_ngs_PowerOfRentedFleetAcquired_019fcb81-08af-7916-921b-453e704b2726" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019fd681-de76-7b53-8d18-858cb403340e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb855-f6a8-71ba-8ca9-d1479341dd96" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019fd681-de76-7b53-8d18-858cb403340e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019fcb48-fc5f-715f-866e-0ef1d4f5d501" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb855-f6a8-71ba-8ca9-d1479341dd96" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019fcb48-fc5f-715f-866e-0ef1d4f5d501" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_019fd3c7-b969-79c2-81a8-bfbfbb9b4c21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb855-f6a8-71ba-8ca9-d1479341dd96" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_019fd3c7-b969-79c2-81a8-bfbfbb9b4c21" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_019fcb81-3106-77fc-8218-7d058dca5481" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb855-f6a8-71ba-8ca9-d1479341dd96" xlink:to="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_019fcb81-3106-77fc-8218-7d058dca5481" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019fce18-f88e-7b69-9191-95885be0c20f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb855-f6a8-71ba-8ca9-d1479341dd96" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019fce18-f88e-7b69-9191-95885be0c20f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019fcb81-3106-76ef-8c47-3ee8fd9160bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb855-f6a8-71ba-8ca9-d1479341dd96" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019fcb81-3106-76ef-8c47-3ee8fd9160bd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_019fcb81-3106-7659-b56d-78ba04c054df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb855-f6a8-71ba-8ca9-d1479341dd96" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_019fcb81-3106-7659-b56d-78ba04c054df" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_019fcb81-3106-74e3-97ed-df058837e6be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb855-f6a8-71ba-8ca9-d1479341dd96" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_019fcb81-3106-74e3-97ed-df058837e6be" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/BusinessCombinationScheduleofBusinessCombinationContingentConsiderationDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#BusinessCombinationScheduleofBusinessCombinationContingentConsiderationDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/BusinessCombinationScheduleofBusinessCombinationContingentConsiderationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019fb84a-f7f1-7543-9214-05d785027e32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019eb697-a4c7-7c99-8af2-df4d97a0b33e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb84a-f7f1-7543-9214-05d785027e32" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019eb697-a4c7-7c99-8af2-df4d97a0b33e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019eb69a-e7ca-7a73-b219-032a6f54a0ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019eb697-a4c7-7c99-8af2-df4d97a0b33e" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019eb69a-e7ca-7a73-b219-032a6f54a0ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019eb69a-e7ca-7a73-b219-032a6f54a0ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019eb69a-e7ca-7a73-b219-032a6f54a0ff" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019eb69a-e7ca-7a73-b219-032a6f54a0ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019eb69a-e7ca-7d07-8501-f98243f40476" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019eb69a-e7ca-7a73-b219-032a6f54a0ff" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019eb69a-e7ca-7d07-8501-f98243f40476" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_FlatrockAcquisitionMember_019eb714-67f9-7cbb-9581-0ea3da465f22" xlink:href="ngs-20260630.xsd#ngs_FlatrockAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019eb69a-e7ca-7d07-8501-f98243f40476" xlink:to="loc_ngs_FlatrockAcquisitionMember_019eb714-67f9-7cbb-9581-0ea3da465f22" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_019fb84a-f7f1-7385-b1ce-d6e83ad0048b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb84a-f7f1-7543-9214-05d785027e32" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_019fb84a-f7f1-7385-b1ce-d6e83ad0048b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019fb84a-f7f1-70eb-b085-c9b32ec43cdb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb84a-f7f1-7543-9214-05d785027e32" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_019fb84a-f7f1-70eb-b085-c9b32ec43cdb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019fb84a-f7f1-7496-85b1-cacefd8b90c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb84a-f7f1-7543-9214-05d785027e32" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019fb84a-f7f1-7496-85b1-cacefd8b90c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019fb84a-f7f1-7ee1-ba57-b42bca029f63" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb84a-f7f1-7543-9214-05d785027e32" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_019fb84a-f7f1-7ee1-ba57-b42bca029f63" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_019fb84d-e28a-7cca-87f6-da26104b179c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb84a-f7f1-7543-9214-05d785027e32" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_019fb84d-e28a-7cca-87f6-da26104b179c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019fb84d-e28a-7209-b116-5647c9240a68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb84a-f7f1-7543-9214-05d785027e32" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019fb84d-e28a-7209-b116-5647c9240a68" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/BusinessCombinationScheduleofBusinessCombinationDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#BusinessCombinationScheduleofBusinessCombinationDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/BusinessCombinationScheduleofBusinessCombinationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fb848-769a-79ee-9f78-6bfdbd3c708b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fb848-769a-79ee-9f78-6bfdbd3c708b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fb848-769a-7d62-8a89-9a0c5a6a2ea5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fb848-769a-79ee-9f78-6bfdbd3c708b" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fb848-769a-7d62-8a89-9a0c5a6a2ea5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fb848-769a-7d62-8a89-9a0c5a6a2ea5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fb848-769a-7d62-8a89-9a0c5a6a2ea5" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fb848-769a-7d62-8a89-9a0c5a6a2ea5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fb848-769a-709c-a3c3-2bc36d1a5337" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fb848-769a-7d62-8a89-9a0c5a6a2ea5" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fb848-769a-709c-a3c3-2bc36d1a5337" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_FlatrockAcquisitionMember_019fb848-769a-7b94-b2c5-d012d01d2cc1" xlink:href="ngs-20260630.xsd#ngs_FlatrockAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fb848-769a-709c-a3c3-2bc36d1a5337" xlink:to="loc_ngs_FlatrockAcquisitionMember_019fb848-769a-7b94-b2c5-d012d01d2cc1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_019fb848-769a-7f85-b9a7-cd02507ddd03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_019fb848-769a-7f85-b9a7-cd02507ddd03" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_019fb848-769a-7ccf-bfd2-a8bbfdf9272f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_019fb848-769a-7ccf-bfd2-a8bbfdf9272f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_019fb848-769a-7c4f-b354-7d1d5164f9a7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_019fb848-769a-7c4f-b354-7d1d5164f9a7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_019fb848-769a-73aa-b22e-d1e21f6fcece" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_019fb848-769a-73aa-b22e-d1e21f6fcece" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_BusinessCombinationRecognizedAssetAcquiredRentalEquipment_019fb848-769a-71ed-911b-2c4e6901281c" xlink:href="ngs-20260630.xsd#ngs_BusinessCombinationRecognizedAssetAcquiredRentalEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_ngs_BusinessCombinationRecognizedAssetAcquiredRentalEquipment_019fb848-769a-71ed-911b-2c4e6901281c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019fb848-769a-77af-9ed6-213596608d40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_019fb848-769a-77af-9ed6-213596608d40" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_019fb848-769a-78ea-9cc8-51dc5a0276ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_019fb848-769a-78ea-9cc8-51dc5a0276ab" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019fb848-769a-72b4-8d82-9b2cdb85a477" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_Goodwill_019fb848-769a-72b4-8d82-9b2cdb85a477" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_019fb848-769a-7cb4-8e6f-d95d4ffee48a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_019fb848-769a-7cb4-8e6f-d95d4ffee48a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_019fb848-769a-73fb-9ed9-ee305ce73cca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_019fb848-769a-73fb-9ed9-ee305ce73cca" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedLabilities_019fb848-769a-79c9-a6e2-e02d616f3db8" xlink:href="ngs-20260630.xsd#ngs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedLabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_ngs_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccruedLabilities_019fb848-769a-79c9-a6e2-e02d616f3db8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_019fb848-769a-7d81-b8cf-fb9ae240b3bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_019fb848-769a-7d81-b8cf-fb9ae240b3bc" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_019fb848-769a-7107-b1f6-2c94ff004973" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_019fb848-769a-7107-b1f6-2c94ff004973" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_019fb848-769a-7ab7-863c-24b468a51a17" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fb848-769a-7f5c-85cf-72eeadd42af7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_019fb848-769a-7ab7-863c-24b468a51a17" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/BusinessCombinationScheduleofTransactionCostsDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#BusinessCombinationScheduleofTransactionCostsDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/BusinessCombinationScheduleofTransactionCostsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019fcdd5-1c96-79d2-858f-8b972f12c4be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fcdd5-1c96-79e8-b160-ffb34c82d153" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fcdd5-1c96-79d2-858f-8b972f12c4be" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fcdd5-1c96-79e8-b160-ffb34c82d153" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fcdd5-1c96-78ba-b6ac-774fdcd56b43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fcdd5-1c96-79e8-b160-ffb34c82d153" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fcdd5-1c96-78ba-b6ac-774fdcd56b43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcdd5-1c96-78ba-b6ac-774fdcd56b43_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fcdd5-1c96-78ba-b6ac-774fdcd56b43" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcdd5-1c96-78ba-b6ac-774fdcd56b43_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcdd5-1c96-76e3-a986-423aeb5c8b84" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fcdd5-1c96-78ba-b6ac-774fdcd56b43" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcdd5-1c96-76e3-a986-423aeb5c8b84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_FlatrockAcquisitionMember_019fcdd5-1c96-731e-a647-0ee70189c0af" xlink:href="ngs-20260630.xsd#ngs_FlatrockAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fcdd5-1c96-76e3-a986-423aeb5c8b84" xlink:to="loc_ngs_FlatrockAcquisitionMember_019fcdd5-1c96-731e-a647-0ee70189c0af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfessionalFees_019fcdd5-1c96-7364-af38-c2580ba1c28a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProfessionalFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fcdd5-1c96-79d2-858f-8b972f12c4be" xlink:to="loc_us-gaap_ProfessionalFees_019fcdd5-1c96-7364-af38-c2580ba1c28a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_OtherAcquisitionCosts_019fcdd7-4964-78aa-aece-6714e0cf10d9" xlink:href="ngs-20260630.xsd#ngs_OtherAcquisitionCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fcdd5-1c96-79d2-858f-8b972f12c4be" xlink:to="loc_ngs_OtherAcquisitionCosts_019fcdd7-4964-78aa-aece-6714e0cf10d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_019fcdd5-1c96-77df-922b-6c19f9c2af10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fcdd5-1c96-79d2-858f-8b972f12c4be" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_019fcdd5-1c96-77df-922b-6c19f9c2af10" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/BusinessCombinationScheduleofBusinessCombinationProFormaInformationDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#BusinessCombinationScheduleofBusinessCombinationProFormaInformationDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/BusinessCombinationScheduleofBusinessCombinationProFormaInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019fa481-1b10-7c28-ade8-1a848661195a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fa481-1b10-7f16-9aeb-7eee59d44477" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fa481-1b10-7c28-ade8-1a848661195a" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fa481-1b10-7f16-9aeb-7eee59d44477" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fa481-1b10-74b3-a2c0-f76c654fda7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_019fa481-1b10-7f16-9aeb-7eee59d44477" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fa481-1b10-74b3-a2c0-f76c654fda7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fa481-1b10-74b3-a2c0-f76c654fda7d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fa481-1b10-74b3-a2c0-f76c654fda7d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fa481-1b10-74b3-a2c0-f76c654fda7d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fa481-1b10-72bd-b614-5c542a2a8265" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fa481-1b10-74b3-a2c0-f76c654fda7d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fa481-1b10-72bd-b614-5c542a2a8265" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_FlatrockAcquisitionMember_019fcb4b-17d0-76e2-8199-0b3c535f492a" xlink:href="ngs-20260630.xsd#ngs_FlatrockAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fa481-1b10-72bd-b614-5c542a2a8265" xlink:to="loc_ngs_FlatrockAcquisitionMember_019fcb4b-17d0-76e2-8199-0b3c535f492a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_019fa481-1b10-7b0d-844a-c775331808db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fa481-1b10-7c28-ade8-1a848661195a" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_019fa481-1b10-7b0d-844a-c775331808db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_019fa481-1b10-79bd-a93e-fbcab7b326ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019fa481-1b10-7c28-ade8-1a848661195a" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_019fa481-1b10-79bd-a93e-fbcab7b326ed" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/TradeAccountsReceivableScheduleofTradeAccountsReceivableDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#TradeAccountsReceivableScheduleofTradeAccountsReceivableDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/TradeAccountsReceivableScheduleofTradeAccountsReceivableDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_019e471f-07b2-7bd3-acfa-d22ea1e2e6da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_019e471f-07b2-7fac-9b47-bbc1ec54c118" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_019e471f-07b2-7bd3-acfa-d22ea1e2e6da" xlink:to="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_019e471f-07b2-7fac-9b47-bbc1ec54c118" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019e471f-07b2-7218-beb8-eeed4987e0ca" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable_019e471f-07b2-7fac-9b47-bbc1ec54c118" xlink:to="loc_srt_ProductOrServiceAxis_019e471f-07b2-7218-beb8-eeed4987e0ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e471f-07b2-7218-beb8-eeed4987e0ca_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019e471f-07b2-7218-beb8-eeed4987e0ca" xlink:to="loc_srt_ProductsAndServicesDomain_019e471f-07b2-7218-beb8-eeed4987e0ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e471f-07b2-7385-90bc-4563356ec6eb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019e471f-07b2-7218-beb8-eeed4987e0ca" xlink:to="loc_srt_ProductsAndServicesDomain_019e471f-07b2-7385-90bc-4563356ec6eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RentalMember_019e471f-07b2-7ef7-99dd-9cbe710b58c7" xlink:href="ngs-20260630.xsd#ngs_RentalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e471f-07b2-7385-90bc-4563356ec6eb" xlink:to="loc_ngs_RentalMember_019e471f-07b2-7ef7-99dd-9cbe710b58c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_SalesAndAftermarketServicesMember_019e471f-07b2-7e1a-9221-5f375a982ebf" xlink:href="ngs-20260630.xsd#ngs_SalesAndAftermarketServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e471f-07b2-7385-90bc-4563356ec6eb" xlink:to="loc_ngs_SalesAndAftermarketServicesMember_019e471f-07b2-7e1a-9221-5f375a982ebf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrentAbstract_019e471f-07b2-7b63-92d1-5694e9e92366" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems_019e471f-07b2-7bd3-acfa-d22ea1e2e6da" xlink:to="loc_us-gaap_AccountsReceivableNetCurrentAbstract_019e471f-07b2-7b63-92d1-5694e9e92366" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableGrossCurrent_019e471f-07b2-76bd-80b9-7dc3cb8bbca7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableGrossCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsReceivableNetCurrentAbstract_019e471f-07b2-7b63-92d1-5694e9e92366" xlink:to="loc_us-gaap_AccountsReceivableGrossCurrent_019e471f-07b2-76bd-80b9-7dc3cb8bbca7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019e471f-07b2-7ea9-9df1-476afabd0131" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsReceivableNetCurrentAbstract_019e471f-07b2-7b63-92d1-5694e9e92366" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019e471f-07b2-7ea9-9df1-476afabd0131" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019e471f-07b2-7040-8505-200903f60a97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsReceivableNetCurrentAbstract_019e471f-07b2-7b63-92d1-5694e9e92366" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019e471f-07b2-7040-8505-200903f60a97" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/TradeAccountsReceivableNarrativeDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#TradeAccountsReceivableNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/TradeAccountsReceivableNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_019e471f-07b2-7da7-b94c-b667145d9696" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_019e471f-07b2-73ac-9005-586400973bb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019e471f-07b2-7da7-b94c-b667145d9696" xlink:to="loc_us-gaap_ConcentrationRiskTable_019e471f-07b2-73ac-9005-586400973bb1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019e471f-07b2-76e1-a6e9-8dcc50fce0d6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019e471f-07b2-73ac-9005-586400973bb1" xlink:to="loc_srt_MajorCustomersAxis_019e471f-07b2-76e1-a6e9-8dcc50fce0d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019e471f-07b2-76e1-a6e9-8dcc50fce0d6_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019e471f-07b2-76e1-a6e9-8dcc50fce0d6" xlink:to="loc_srt_NameOfMajorCustomerDomain_019e471f-07b2-76e1-a6e9-8dcc50fce0d6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019e471f-07b2-7816-bfc2-ffc978f42af8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019e471f-07b2-76e1-a6e9-8dcc50fce0d6" xlink:to="loc_srt_NameOfMajorCustomerDomain_019e471f-07b2-7816-bfc2-ffc978f42af8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_OxyAndDevonMember_019e471f-07b2-7fc8-aec5-374b79d344c6" xlink:href="ngs-20260630.xsd#ngs_OxyAndDevonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019e471f-07b2-7816-bfc2-ffc978f42af8" xlink:to="loc_ngs_OxyAndDevonMember_019e471f-07b2-7fc8-aec5-374b79d344c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e471f-07b2-728a-8629-ad4751033ccc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019e471f-07b2-73ac-9005-586400973bb1" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e471f-07b2-728a-8629-ad4751033ccc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e471f-07b2-728a-8629-ad4751033ccc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e471f-07b2-728a-8629-ad4751033ccc" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e471f-07b2-728a-8629-ad4751033ccc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e471f-07b2-7081-8d23-ee6f2051b8e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019e471f-07b2-728a-8629-ad4751033ccc" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e471f-07b2-7081-8d23-ee6f2051b8e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_SalesRevenueGoodsNetAndRentalIncomeMember_019e471f-07b2-7077-9dfc-928a527794c9" xlink:href="ngs-20260630.xsd#ngs_SalesRevenueGoodsNetAndRentalIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e471f-07b2-7081-8d23-ee6f2051b8e1" xlink:to="loc_ngs_SalesRevenueGoodsNetAndRentalIncomeMember_019e471f-07b2-7077-9dfc-928a527794c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_019e471f-07b2-70cb-9d41-6a686dbce8cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019e471f-07b2-7081-8d23-ee6f2051b8e1" xlink:to="loc_us-gaap_AccountsReceivableMember_019e471f-07b2-70cb-9d41-6a686dbce8cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019e471f-07b2-79d0-9709-83a26535e621" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019e471f-07b2-73ac-9005-586400973bb1" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019e471f-07b2-79d0-9709-83a26535e621" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e471f-07b2-79d0-9709-83a26535e621_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019e471f-07b2-79d0-9709-83a26535e621" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e471f-07b2-79d0-9709-83a26535e621_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019e471f-07b2-7f6c-ac47-dbcaba8c87e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019e471f-07b2-79d0-9709-83a26535e621" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019e471f-07b2-7f6c-ac47-dbcaba8c87e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019e471f-07b2-79f9-8a4f-b23d158d6109" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019e471f-07b2-7f6c-ac47-dbcaba8c87e0" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019e471f-07b2-79f9-8a4f-b23d158d6109" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019e471f-07b2-72f5-bf54-0c8fc8485759" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019e471f-07b2-7da7-b94c-b667145d9696" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019e471f-07b2-72f5-bf54-0c8fc8485759" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/AssetsHeldforSaleandRestructuringActivitiesDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#AssetsHeldforSaleandRestructuringActivitiesDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/AssetsHeldforSaleandRestructuringActivitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e471f-07b2-7ecc-b005-fc19428374a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e471f-07b2-79c9-8bfd-866e2e6f15c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e471f-07b2-7ecc-b005-fc19428374a2" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e471f-07b2-79c9-8bfd-866e2e6f15c9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-07b2-7455-875d-400466f79aa2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_019e471f-07b2-79c9-8bfd-866e2e6f15c9" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-07b2-7455-875d-400466f79aa2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7455-875d-400466f79aa2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-07b2-7455-875d-400466f79aa2" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7455-875d-400466f79aa2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-70c2-a64e-6d3ef8b74195" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-07b2-7455-875d-400466f79aa2" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-70c2-a64e-6d3ef8b74195" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandAndBuildingMember_019e471f-07b2-7586-be73-05a8a58bc944" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandAndBuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-70c2-a64e-6d3ef8b74195" xlink:to="loc_us-gaap_LandAndBuildingMember_019e471f-07b2-7586-be73-05a8a58bc944" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_019e471f-07b2-778c-8015-53769b56c02b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e471f-07b2-7ecc-b005-fc19428374a2" xlink:to="loc_us-gaap_AssetImpairmentCharges_019e471f-07b2-778c-8015-53769b56c02b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsHeldForSaleNotPartOfDisposalGroupCurrent_019e471f-07b2-76ad-b0b2-689fd02e331b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsHeldForSaleNotPartOfDisposalGroupCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e471f-07b2-7ecc-b005-fc19428374a2" xlink:to="loc_us-gaap_AssetsHeldForSaleNotPartOfDisposalGroupCurrent_019e471f-07b2-76ad-b0b2-689fd02e331b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminated_019e471f-07b2-727b-a306-a5a007b72f48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminated"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e471f-07b2-7ecc-b005-fc19428374a2" xlink:to="loc_us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminated_019e471f-07b2-727b-a306-a5a007b72f48" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeveranceCosts1_019e471f-07b2-7034-9ac5-9ff8b54e911a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeveranceCosts1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_019e471f-07b2-7ecc-b005-fc19428374a2" xlink:to="loc_us-gaap_SeveranceCosts1_019e471f-07b2-7034-9ac5-9ff8b54e911a" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/RentalEquipmentScheduleofRentalEquipmentDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#RentalEquipmentScheduleofRentalEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/RentalEquipmentScheduleofRentalEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-07b2-7a63-8022-fab3babdaee3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-07b2-7852-9f7b-d535dd8ec3c8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-07b2-7a63-8022-fab3babdaee3" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-07b2-7852-9f7b-d535dd8ec3c8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-07b2-7cb1-92fd-4f3d4d50a24a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-07b2-7852-9f7b-d535dd8ec3c8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-07b2-7cb1-92fd-4f3d4d50a24a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7cb1-92fd-4f3d4d50a24a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-07b2-7cb1-92fd-4f3d4d50a24a" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7cb1-92fd-4f3d4d50a24a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7c2a-8588-0c2b193052bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-07b2-7cb1-92fd-4f3d4d50a24a" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7c2a-8588-0c2b193052bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RentalCompressorUnitMember_019e471f-07b2-72ba-88f3-a00b8797b5d5" xlink:href="ngs-20260630.xsd#ngs_RentalCompressorUnitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7c2a-8588-0c2b193052bd" xlink:to="loc_ngs_RentalCompressorUnitMember_019e471f-07b2-72ba-88f3-a00b8797b5d5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RentalCompressorUnitWorkInProgressMember_019e471f-07b2-71ea-a673-0dd34e09df43" xlink:href="ngs-20260630.xsd#ngs_RentalCompressorUnitWorkInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7c2a-8588-0c2b193052bd" xlink:to="loc_ngs_RentalCompressorUnitWorkInProgressMember_019e471f-07b2-71ea-a673-0dd34e09df43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RentalEquipmentGross_019e471f-07b2-7ee3-9321-1b95e113cbd4" xlink:href="ngs-20260630.xsd#ngs_RentalEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-07b2-7a63-8022-fab3babdaee3" xlink:to="loc_ngs_RentalEquipmentGross_019e471f-07b2-7ee3-9321-1b95e113cbd4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RentalEquipmentAccumulatedDepreciation_019e471f-07b2-74e7-9e42-4590a8a68a48" xlink:href="ngs-20260630.xsd#ngs_RentalEquipmentAccumulatedDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-07b2-7a63-8022-fab3babdaee3" xlink:to="loc_ngs_RentalEquipmentAccumulatedDepreciation_019e471f-07b2-74e7-9e42-4590a8a68a48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RentalEquipmentNet_019e471f-07b2-7031-a5fd-15fc5695d55b" xlink:href="ngs-20260630.xsd#ngs_RentalEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-07b2-7a63-8022-fab3babdaee3" xlink:to="loc_ngs_RentalEquipmentNet_019e471f-07b2-7031-a5fd-15fc5695d55b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/RentalEquipmentNarrativeDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#RentalEquipmentNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/RentalEquipmentNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-07b2-7737-9dc5-5af82d59af1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-07b2-770e-8c6f-79e6ba01f796" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-07b2-7737-9dc5-5af82d59af1c" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-07b2-770e-8c6f-79e6ba01f796" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-07b2-7f29-9dd6-b34c83de91e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-07b2-770e-8c6f-79e6ba01f796" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-07b2-7f29-9dd6-b34c83de91e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7f29-9dd6-b34c83de91e0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-07b2-7f29-9dd6-b34c83de91e0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7f29-9dd6-b34c83de91e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7508-bc34-5b19aac334b2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-07b2-7f29-9dd6-b34c83de91e0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7508-bc34-5b19aac334b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RentalEquipmentMember_019e471f-07b2-7e95-8111-57cc768e64af" xlink:href="ngs-20260630.xsd#ngs_RentalEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-07b2-7508-bc34-5b19aac334b2" xlink:to="loc_ngs_RentalEquipmentMember_019e471f-07b2-7e95-8111-57cc768e64af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RentalEquipmentUnitsRetired_019e471f-07b2-7a47-9c1a-3e38d9c72a4d" xlink:href="ngs-20260630.xsd#ngs_RentalEquipmentUnitsRetired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-07b2-7737-9dc5-5af82d59af1c" xlink:to="loc_ngs_RentalEquipmentUnitsRetired_019e471f-07b2-7a47-9c1a-3e38d9c72a4d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RentalEquipmentHorsepowerRetired_019e471f-07b2-7c5b-a881-dd2e9e30f98f" xlink:href="ngs-20260630.xsd#ngs_RentalEquipmentHorsepowerRetired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-07b2-7737-9dc5-5af82d59af1c" xlink:to="loc_ngs_RentalEquipmentHorsepowerRetired_019e471f-07b2-7c5b-a881-dd2e9e30f98f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentDisposals_019e471f-07b2-70da-8243-68146e5103ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentDisposals"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-07b2-7737-9dc5-5af82d59af1c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentDisposals_019e471f-07b2-70da-8243-68146e5103ea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_019e471f-07b2-7b9d-8bbe-50b39cc573b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-07b2-7737-9dc5-5af82d59af1c" xlink:to="loc_us-gaap_Depreciation_019e471f-07b2-7b9d-8bbe-50b39cc573b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestCostsCapitalized_019e471f-07b2-7e3a-aee4-e048dc886e4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestCostsCapitalized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-07b2-7737-9dc5-5af82d59af1c" xlink:to="loc_us-gaap_InterestCostsCapitalized_019e471f-07b2-7e3a-aee4-e048dc886e4f" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/PropertyandEquipmentScheduleofPropertyandNonRentalEquipmentDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#PropertyandEquipmentScheduleofPropertyandNonRentalEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/PropertyandEquipmentScheduleofPropertyandNonRentalEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-088b-79e6-b35f-f842a7169e27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-088b-7d78-89ff-b6c759758ea6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-088b-79e6-b35f-f842a7169e27" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-088b-7d78-89ff-b6c759758ea6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-088b-7247-ab8b-4f71fc4d9878" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-088b-7d78-89ff-b6c759758ea6" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-088b-7247-ab8b-4f71fc4d9878" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-7247-ab8b-4f71fc4d9878_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-088b-7247-ab8b-4f71fc4d9878" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-7247-ab8b-4f71fc4d9878_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-715e-9308-10617908bef4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-088b-7247-ab8b-4f71fc4d9878" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-715e-9308-10617908bef4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandMember_019e471f-088b-7241-b5cc-f469502c2e05" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-715e-9308-10617908bef4" xlink:to="loc_us-gaap_LandMember_019e471f-088b-7241-b5cc-f469502c2e05" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingMember_019e471f-088b-7860-bebd-48fa2302561e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-715e-9308-10617908bef4" xlink:to="loc_us-gaap_BuildingMember_019e471f-088b-7860-bebd-48fa2302561e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019e471f-088b-708f-b633-f5ac91d1fc9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-715e-9308-10617908bef4" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019e471f-088b-708f-b633-f5ac91d1fc9c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_OfficeEquipmentAndFurnitureMember_019e471f-088b-7e34-a313-80715f4ba5be" xlink:href="ngs-20260630.xsd#ngs_OfficeEquipmentAndFurnitureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-715e-9308-10617908bef4" xlink:to="loc_ngs_OfficeEquipmentAndFurnitureMember_019e471f-088b-7e34-a313-80715f4ba5be" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_019e471f-088b-719c-858b-9c6a455946f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-715e-9308-10617908bef4" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_019e471f-088b-719c-858b-9c6a455946f7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_019e471f-088b-7c06-ae76-59d0deece362" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-715e-9308-10617908bef4" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_019e471f-088b-7c06-ae76-59d0deece362" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VehiclesMember_019e471f-088b-7d85-b513-769599ed9924" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VehiclesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-715e-9308-10617908bef4" xlink:to="loc_us-gaap_VehiclesMember_019e471f-088b-7d85-b513-769599ed9924" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_WorkInProgressMember_019e471f-088b-79d8-837b-60228e2afdcb" xlink:href="ngs-20260630.xsd#ngs_WorkInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-715e-9308-10617908bef4" xlink:to="loc_ngs_WorkInProgressMember_019e471f-088b-79d8-837b-60228e2afdcb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019e471f-088b-77ea-8ba2-b85a6306d473" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-088b-79e6-b35f-f842a7169e27" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019e471f-088b-77ea-8ba2-b85a6306d473" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019e471f-088b-716f-ae3f-404d0584e4f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-088b-79e6-b35f-f842a7169e27" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019e471f-088b-716f-ae3f-404d0584e4f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019e471f-088b-7fe9-a64f-23bb6efa5cc2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-088b-79e6-b35f-f842a7169e27" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019e471f-088b-7fe9-a64f-23bb6efa5cc2" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/PropertyandEquipmentNarrativeDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#PropertyandEquipmentNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/PropertyandEquipmentNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-088b-7c92-9b60-31ceaec64d93" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-088b-79d2-8993-1fe42729ff22" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-088b-7c92-9b60-31ceaec64d93" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-088b-79d2-8993-1fe42729ff22" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-088b-7417-8721-c6a182f55a32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-088b-79d2-8993-1fe42729ff22" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-088b-7417-8721-c6a182f55a32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-7417-8721-c6a182f55a32_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-088b-7417-8721-c6a182f55a32" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-7417-8721-c6a182f55a32_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-7325-ac03-b2e24cac181f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019e471f-088b-7417-8721-c6a182f55a32" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-7325-ac03-b2e24cac181f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_PropertyPlantAndEquipmentExcludingRentalEquipmentMember_019e471f-088b-7800-85e5-65ddede4d274" xlink:href="ngs-20260630.xsd#ngs_PropertyPlantAndEquipmentExcludingRentalEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-7325-ac03-b2e24cac181f" xlink:to="loc_ngs_PropertyPlantAndEquipmentExcludingRentalEquipmentMember_019e471f-088b-7800-85e5-65ddede4d274" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LandAndBuildingMember_019e471f-088b-7a88-af8c-bab0a207104e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LandAndBuildingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019e471f-088b-7325-ac03-b2e24cac181f" xlink:to="loc_us-gaap_LandAndBuildingMember_019e471f-088b-7a88-af8c-bab0a207104e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019e471f-088b-7cba-b474-c97b69aa6c9e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019e471f-088b-79d2-8993-1fe42729ff22" xlink:to="loc_srt_StatementGeographicalAxis_019e471f-088b-7cba-b474-c97b69aa6c9e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e471f-088b-7cba-b474-c97b69aa6c9e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019e471f-088b-7cba-b474-c97b69aa6c9e" xlink:to="loc_srt_SegmentGeographicalDomain_019e471f-088b-7cba-b474-c97b69aa6c9e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019e471f-088b-7e47-aa26-138ff2b15e0e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019e471f-088b-7cba-b474-c97b69aa6c9e" xlink:to="loc_srt_SegmentGeographicalDomain_019e471f-088b-7e47-aa26-138ff2b15e0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_MidlandTexasMember_019e471f-088b-7e8c-b8fe-fa69fca015bf" xlink:href="ngs-20260630.xsd#ngs_MidlandTexasMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019e471f-088b-7e47-aa26-138ff2b15e0e" xlink:to="loc_ngs_MidlandTexasMember_019e471f-088b-7e8c-b8fe-fa69fca015bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_019e471f-088b-776d-94ab-876cdbb4f977" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-088b-7c92-9b60-31ceaec64d93" xlink:to="loc_us-gaap_Depreciation_019e471f-088b-776d-94ab-876cdbb4f977" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsHeldForSaleNotPartOfDisposalGroupCurrent_019e471f-088b-79d9-b32c-d26f22bc4fca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsHeldForSaleNotPartOfDisposalGroupCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019e471f-088b-7c92-9b60-31ceaec64d93" xlink:to="loc_us-gaap_AssetsHeldForSaleNotPartOfDisposalGroupCurrent_019e471f-088b-79d9-b32c-d26f22bc4fca" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/LongTermDebtNarrativeDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#LongTermDebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/LongTermDebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_019e471f-088b-7522-b8f4-a7b583cccbff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_019e471f-088b-7522-b8f4-a7b583cccbff" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019e471f-088b-78a5-9c00-46f667862053" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019e471f-088b-7522-b8f4-a7b583cccbff" xlink:to="loc_us-gaap_CreditFacilityAxis_019e471f-088b-78a5-9c00-46f667862053" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019e471f-088b-78a5-9c00-46f667862053_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019e471f-088b-78a5-9c00-46f667862053" xlink:to="loc_us-gaap_CreditFacilityDomain_019e471f-088b-78a5-9c00-46f667862053_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019e471f-088b-7e44-9e9a-7a5fd78aa193" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019e471f-088b-78a5-9c00-46f667862053" xlink:to="loc_us-gaap_CreditFacilityDomain_019e471f-088b-7e44-9e9a-7a5fd78aa193" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019e471f-088b-7816-a600-fe38e9c893a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019e471f-088b-7e44-9e9a-7a5fd78aa193" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019e471f-088b-7816-a600-fe38e9c893a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019e471f-088b-7e49-a9f5-6079d6bdcf02" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019e471f-088b-7522-b8f4-a7b583cccbff" xlink:to="loc_us-gaap_VariableRateAxis_019e471f-088b-7e49-a9f5-6079d6bdcf02" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019e471f-088b-7e49-a9f5-6079d6bdcf02_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019e471f-088b-7e49-a9f5-6079d6bdcf02" xlink:to="loc_us-gaap_VariableRateDomain_019e471f-088b-7e49-a9f5-6079d6bdcf02_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019e471f-088b-76fd-9259-9b784c3f037e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019e471f-088b-7e49-a9f5-6079d6bdcf02" xlink:to="loc_us-gaap_VariableRateDomain_019e471f-088b-76fd-9259-9b784c3f037e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_FederalFundRateMember_019e471f-088b-7df1-9f50-a13e6477d28a" xlink:href="ngs-20260630.xsd#ngs_FederalFundRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019e471f-088b-76fd-9259-9b784c3f037e" xlink:to="loc_ngs_FederalFundRateMember_019e471f-088b-7df1-9f50-a13e6477d28a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019e471f-088b-7d8d-ba2c-c2e77197f4e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019e471f-088b-76fd-9259-9b784c3f037e" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019e471f-088b-7d8d-ba2c-c2e77197f4e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_BaseRateLoansMember_019e471f-088b-7943-8187-757aba91d035" xlink:href="ngs-20260630.xsd#ngs_BaseRateLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019e471f-088b-76fd-9259-9b784c3f037e" xlink:to="loc_ngs_BaseRateLoansMember_019e471f-088b-7943-8187-757aba91d035" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e471f-088b-7d06-a469-bb49f920d7d7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019e471f-088b-7522-b8f4-a7b583cccbff" xlink:to="loc_srt_RangeAxis_019e471f-088b-7d06-a469-bb49f920d7d7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e471f-088b-7d06-a469-bb49f920d7d7_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019e471f-088b-7d06-a469-bb49f920d7d7" xlink:to="loc_srt_RangeMember_019e471f-088b-7d06-a469-bb49f920d7d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e471f-088b-770e-a26e-6cdf503015a0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019e471f-088b-7d06-a469-bb49f920d7d7" xlink:to="loc_srt_RangeMember_019e471f-088b-770e-a26e-6cdf503015a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e471f-088b-7591-8804-dc421ee40ef8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e471f-088b-770e-a26e-6cdf503015a0" xlink:to="loc_srt_MinimumMember_019e471f-088b-7591-8804-dc421ee40ef8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e471f-088b-7a19-888a-06f82e6f08e7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e471f-088b-770e-a26e-6cdf503015a0" xlink:to="loc_srt_MaximumMember_019e471f-088b-7a19-888a-06f82e6f08e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_019e471f-088b-7424-98eb-cd542dcc7ded" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity_019e471f-088b-7424-98eb-cd542dcc7ded" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFeeAmount_019f63ce-0e26-7ed5-9109-f4184694e7b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_us-gaap_DebtInstrumentFeeAmount_019f63ce-0e26-7ed5-9109-f4184694e7b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityPotentialIncreaseInBorrowingCapacity_019e471f-088b-7220-a668-51c282f94026" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityPotentialIncreaseInBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityPotentialIncreaseInBorrowingCapacity_019e471f-088b-7220-a668-51c282f94026" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityPotentialMaximumBorrowingCapacity_019e471f-088b-7b4f-9540-de2c8fd38d04" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityPotentialMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityPotentialMaximumBorrowingCapacity_019e471f-088b-7b4f-9540-de2c8fd38d04" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019e471f-088b-797a-816c-d39649a09059" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_us-gaap_LineOfCredit_019e471f-088b-797a-816c-d39649a09059" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtWeightedAverageInterestRateOverTime_019e471f-088b-7ecb-8417-338ff3a451de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtWeightedAverageInterestRateOverTime"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_us-gaap_LongTermDebtWeightedAverageInterestRateOverTime_019e471f-088b-7ecb-8417-338ff3a451de" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_019fcb8f-045f-7a07-89aa-6633b0ffa666" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_019fcb8f-045f-7a07-89aa-6633b0ffa666" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019e471f-088b-7bac-94c1-3ddd6c662562" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_019e471f-088b-7bac-94c1-3ddd6c662562" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentOfEligibleAccountsReceivableOwingByNonInvestmentGradeDebtors_019e471f-088b-7574-9227-4da24de6f6c3" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentOfEligibleAccountsReceivableOwingByNonInvestmentGradeDebtors"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentOfEligibleAccountsReceivableOwingByNonInvestmentGradeDebtors_019e471f-088b-7574-9227-4da24de6f6c3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleInventory_019e471f-088b-7279-8b62-c8b0eafec8ff" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleInventory_019e471f-088b-7279-8b62-c8b0eafec8ff" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityNonExceedingCapOfComponentCapacity_019e471f-088b-75e3-b7c0-d4f20317345f" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityNonExceedingCapOfComponentCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityNonExceedingCapOfComponentCapacity_019e471f-088b-75e3-b7c0-d4f20317345f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleCompressorsForExtensionOfCredit_019e471f-088b-7864-8858-caa2a293fa1a" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleCompressorsForExtensionOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleCompressorsForExtensionOfCredit_019e471f-088b-7864-8858-caa2a293fa1a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityTermForDepreciation_019e471f-088b-7455-9b33-674a49872d00" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityTermForDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityTermForDepreciation_019e471f-088b-7455-9b33-674a49872d00" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityCurrentBorrowingCapacityNetLiquidationValueOfPercentageOfEligibleCompressorsForExtensionOfCredit_019e471f-088b-7225-a0c9-2dece5cec1ff" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityCurrentBorrowingCapacityNetLiquidationValueOfPercentageOfEligibleCompressorsForExtensionOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityCurrentBorrowingCapacityNetLiquidationValueOfPercentageOfEligibleCompressorsForExtensionOfCredit_019e471f-088b-7225-a0c9-2dece5cec1ff" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleValueAtCostExcludingAnyCostForCapitalizedInterestOrOtherNonCashCapitalizedCosts_019e471f-088b-7a03-bd50-447d224262a7" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleValueAtCostExcludingAnyCostForCapitalizedInterestOrOtherNonCashCapitalizedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleValueAtCostExcludingAnyCostForCapitalizedInterestOrOtherNonCashCapitalizedCosts_019e471f-088b-7a03-bd50-447d224262a7" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019e471f-088b-7179-a8e7-d9975bf37518" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019e471f-088b-7179-a8e7-d9975bf37518" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019e471f-088b-7034-8f55-5010b61f28d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019e471f-088b-7034-8f55-5010b61f28d9" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityLeverageRatio_019e471f-088b-72d4-af94-1fe5bd8b2db8" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityLeverageRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityLeverageRatio_019e471f-088b-72d4-af94-1fe5bd8b2db8" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityFixedChargeCoverageRatio_019e471f-088b-7913-9f08-84127c7ba031" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityFixedChargeCoverageRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityFixedChargeCoverageRatio_019e471f-088b-7913-9f08-84127c7ba031" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityDefaultTriggerCertainDefaultsOfOtherCompanyIndebtednessAmount_019e471f-088b-7337-a9ab-dff629fec383" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityDefaultTriggerCertainDefaultsOfOtherCompanyIndebtednessAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityDefaultTriggerCertainDefaultsOfOtherCompanyIndebtednessAmount_019e471f-088b-7337-a9ab-dff629fec383" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LineOfCreditFacilityDefaultTriggerRenderingOfCertainJudgmentsAmount_019e471f-088b-7636-be74-3a14e5c07e9a" xlink:href="ngs-20260630.xsd#ngs_LineOfCreditFacilityDefaultTriggerRenderingOfCertainJudgmentsAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019e471f-088b-7c6a-b4a8-45ca66247ebe" xlink:to="loc_ngs_LineOfCreditFacilityDefaultTriggerRenderingOfCertainJudgmentsAmount_019e471f-088b-7636-be74-3a14e5c07e9a" xlink:type="arc" order="20"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/IncomeTaxesDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#IncomeTaxesDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/IncomeTaxesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsLineItems_019e471f-088b-7f1c-ac3b-20f0a08782f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLossCarryforwardsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsTable_019e471f-088b-7dde-b410-98de16bd1841" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLossCarryforwardsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_019e471f-088b-7f1c-ac3b-20f0a08782f8" xlink:to="loc_us-gaap_OperatingLossCarryforwardsTable_019e471f-088b-7dde-b410-98de16bd1841" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodAxis_019e471f-088b-7e74-9566-2f1254c2ada5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OperatingLossCarryforwardsTable_019e471f-088b-7dde-b410-98de16bd1841" xlink:to="loc_us-gaap_TaxPeriodAxis_019e471f-088b-7e74-9566-2f1254c2ada5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_019e471f-088b-7e74-9566-2f1254c2ada5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxPeriodAxis_019e471f-088b-7e74-9566-2f1254c2ada5" xlink:to="loc_us-gaap_TaxPeriodDomain_019e471f-088b-7e74-9566-2f1254c2ada5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxPeriodDomain_019e471f-088b-7413-82d5-f38d2a037844" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxPeriodAxis_019e471f-088b-7e74-9566-2f1254c2ada5" xlink:to="loc_us-gaap_TaxPeriodDomain_019e471f-088b-7413-82d5-f38d2a037844" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxYear2019Member_019e471f-088b-7146-8a27-0265a07dfd48" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TaxYear2019Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxPeriodDomain_019e471f-088b-7413-82d5-f38d2a037844" xlink:to="loc_us-gaap_TaxYear2019Member_019e471f-088b-7146-8a27-0265a07dfd48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_TaxYear20152016And2017Member_019e471f-088b-7472-80a9-c0d8f8df3d64" xlink:href="ngs-20260630.xsd#ngs_TaxYear20152016And2017Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxPeriodDomain_019e471f-088b-7413-82d5-f38d2a037844" xlink:to="loc_ngs_TaxYear20152016And2017Member_019e471f-088b-7472-80a9-c0d8f8df3d64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesReceivable_019e471f-088b-7429-9796-273f8614089e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_019e471f-088b-7f1c-ac3b-20f0a08782f8" xlink:to="loc_us-gaap_IncomeTaxesReceivable_019e471f-088b-7429-9796-273f8614089e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_ProceedsFromIncomeTaxRefundsAndInterest_019e471f-088b-723b-9311-22e15e841b7a" xlink:href="ngs-20260630.xsd#ngs_ProceedsFromIncomeTaxRefundsAndInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_019e471f-088b-7f1c-ac3b-20f0a08782f8" xlink:to="loc_ngs_ProceedsFromIncomeTaxRefundsAndInterest_019e471f-088b-723b-9311-22e15e841b7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIncomeTaxRefunds_019e471f-088b-7c9c-9bae-51c4ffe329dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIncomeTaxRefunds"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_019e471f-088b-7f1c-ac3b-20f0a08782f8" xlink:to="loc_us-gaap_ProceedsFromIncomeTaxRefunds_019e471f-088b-7c9c-9bae-51c4ffe329dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOperating_019e471f-088b-7774-9853-a76ae226ba78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_019e471f-088b-7f1c-ac3b-20f0a08782f8" xlink:to="loc_us-gaap_InterestIncomeOperating_019e471f-088b-7774-9853-a76ae226ba78" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate_019fd827-22aa-7eb7-89d2-4442df7ddb59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_019e471f-088b-7f1c-ac3b-20f0a08782f8" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate_019fd827-22aa-7eb7-89d2-4442df7ddb59" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/StockholdersEquityNarrativeDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#StockholdersEquityNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/StockholdersEquityNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019fd259-3cd4-711b-96d2-462e1c6aeff4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019fd259-3cd4-7fdb-8de3-dc186fd2647e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019fd259-3cd4-711b-96d2-462e1c6aeff4" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019fd259-3cd4-7fdb-8de3-dc186fd2647e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019fd259-3cd4-7eb9-9739-303ff8ceedaa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019fd259-3cd4-7fdb-8de3-dc186fd2647e" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019fd259-3cd4-7eb9-9739-303ff8ceedaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd259-3cd4-7eb9-9739-303ff8ceedaa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd259-3cd4-7eb9-9739-303ff8ceedaa" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd259-3cd4-7eb9-9739-303ff8ceedaa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd259-3cd4-731c-b8a4-a5c0a1af0dbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019fd259-3cd4-7eb9-9739-303ff8ceedaa" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd259-3cd4-731c-b8a4-a5c0a1af0dbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_FlatrockAcquisitionMember_019fd259-3cd4-7bf2-91f4-7a3d15a8eadc" xlink:href="ngs-20260630.xsd#ngs_FlatrockAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019fd259-3cd4-731c-b8a4-a5c0a1af0dbb" xlink:to="loc_ngs_FlatrockAcquisitionMember_019fd259-3cd4-7bf2-91f4-7a3d15a8eadc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019fd6ab-19fe-783c-8705-c7bbd451957e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019fd259-3cd4-711b-96d2-462e1c6aeff4" xlink:to="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_019fd6ab-19fe-783c-8705-c7bbd451957e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/RevenuesfromCustomersScheduleofDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#RevenuesfromCustomersScheduleofDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/RevenuesfromCustomersScheduleofDisaggregationofRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019e471f-088b-70f9-8508-1998bd1a30f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019e471f-088b-72eb-a804-3ec2829dd275" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e471f-088b-70f9-8508-1998bd1a30f0" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019e471f-088b-72eb-a804-3ec2829dd275" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019e471f-088b-7b37-847b-383fe5087c00" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019e471f-088b-72eb-a804-3ec2829dd275" xlink:to="loc_srt_ProductOrServiceAxis_019e471f-088b-7b37-847b-383fe5087c00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e471f-088b-7b37-847b-383fe5087c00_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019e471f-088b-7b37-847b-383fe5087c00" xlink:to="loc_srt_ProductsAndServicesDomain_019e471f-088b-7b37-847b-383fe5087c00_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019e471f-088b-7fdb-b769-ed3d75b4a3b3" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019e471f-088b-7b37-847b-383fe5087c00" xlink:to="loc_srt_ProductsAndServicesDomain_019e471f-088b-7fdb-b769-ed3d75b4a3b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_PartsMember_019e471f-088b-7dc9-8ec1-92caa087a94c" xlink:href="ngs-20260630.xsd#ngs_PartsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e471f-088b-7fdb-b769-ed3d75b4a3b3" xlink:to="loc_ngs_PartsMember_019e471f-088b-7dc9-8ec1-92caa087a94c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductAndServiceOtherMember_019e471f-088b-706b-a4ea-a4ccd227c5df" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductAndServiceOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e471f-088b-7fdb-b769-ed3d75b4a3b3" xlink:to="loc_us-gaap_ProductAndServiceOtherMember_019e471f-088b-706b-a4ea-a4ccd227c5df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_ProductSalesMember_019e471f-088b-783c-8eb9-a1e23b71a681" xlink:href="ngs-20260630.xsd#ngs_ProductSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e471f-088b-7fdb-b769-ed3d75b4a3b3" xlink:to="loc_ngs_ProductSalesMember_019e471f-088b-783c-8eb9-a1e23b71a681" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_AftermarketServicesMember_019e471f-088b-76e5-8345-a4de2c3ca959" xlink:href="ngs-20260630.xsd#ngs_AftermarketServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019e471f-088b-7fdb-b769-ed3d75b4a3b3" xlink:to="loc_ngs_AftermarketServicesMember_019e471f-088b-76e5-8345-a4de2c3ca959" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RentalIncomeNonoperating_019e471f-088b-7a44-8b64-18a24d34b41a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RentalIncomeNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e471f-088b-70f9-8508-1998bd1a30f0" xlink:to="loc_us-gaap_RentalIncomeNonoperating_019e471f-088b-7a44-8b64-18a24d34b41a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e471f-088b-77f6-9d31-5d8205b9dc4e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e471f-088b-70f9-8508-1998bd1a30f0" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019e471f-088b-77f6-9d31-5d8205b9dc4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019e471f-088b-7612-af4f-5d49d6396c0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019e471f-088b-70f9-8508-1998bd1a30f0" xlink:to="loc_us-gaap_Revenues_019e471f-088b-7612-af4f-5d49d6396c0b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/StockBasedandOtherLongTermIncentiveCompensationNarrativeDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#StockBasedandOtherLongTermIncentiveCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/StockBasedandOtherLongTermIncentiveCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-7acd-b922-2c83e0242fa6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-73cb-8c5b-2722a6cd24ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-7acd-b922-2c83e0242fa6" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-73cb-8c5b-2722a6cd24ce" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019e471f-088b-799b-af3a-09c2b60d2045" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-73cb-8c5b-2722a6cd24ce" xlink:to="loc_us-gaap_PlanNameAxis_019e471f-088b-799b-af3a-09c2b60d2045" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019e471f-088b-799b-af3a-09c2b60d2045_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019e471f-088b-799b-af3a-09c2b60d2045" xlink:to="loc_us-gaap_PlanNameDomain_019e471f-088b-799b-af3a-09c2b60d2045_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019e471f-088b-7f29-8706-71cc8dcd000a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019e471f-088b-799b-af3a-09c2b60d2045" xlink:to="loc_us-gaap_PlanNameDomain_019e471f-088b-7f29-8706-71cc8dcd000a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_EquityIncentivePlanMember_019e471f-088b-7e4e-9319-5d3ffad3e059" xlink:href="ngs-20260630.xsd#ngs_EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019e471f-088b-7f29-8706-71cc8dcd000a" xlink:to="loc_ngs_EquityIncentivePlanMember_019e471f-088b-7e4e-9319-5d3ffad3e059" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e471f-088b-7795-9d9c-3cc5ffe239f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-73cb-8c5b-2722a6cd24ce" xlink:to="loc_us-gaap_AwardTypeAxis_019e471f-088b-7795-9d9c-3cc5ffe239f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-7795-9d9c-3cc5ffe239f5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019e471f-088b-7795-9d9c-3cc5ffe239f5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-7795-9d9c-3cc5ffe239f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-72db-85af-f52699946b7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019e471f-088b-7795-9d9c-3cc5ffe239f5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-72db-85af-f52699946b7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_019e471f-088b-738b-9ef1-61e8b147f307" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-72db-85af-f52699946b7d" xlink:to="loc_us-gaap_RestrictedStockMember_019e471f-088b-738b-9ef1-61e8b147f307" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019e471f-088b-780b-a18c-aaa3d894124e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-72db-85af-f52699946b7d" xlink:to="loc_us-gaap_PerformanceSharesMember_019e471f-088b-780b-a18c-aaa3d894124e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019e471f-088b-7483-8986-1dbde0a02220" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-73cb-8c5b-2722a6cd24ce" xlink:to="loc_srt_TitleOfIndividualAxis_019e471f-088b-7483-8986-1dbde0a02220" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019e471f-088b-7483-8986-1dbde0a02220_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019e471f-088b-7483-8986-1dbde0a02220" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019e471f-088b-7483-8986-1dbde0a02220_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019e471f-088b-72eb-952e-0ac7a80b794e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019e471f-088b-7483-8986-1dbde0a02220" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019e471f-088b-72eb-952e-0ac7a80b794e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_ChiefExecutiveOfficerChiefOperatingOfficerAndChiefFinancialOfficerMember_019e471f-088b-7058-8771-2a25e5816b36" xlink:href="ngs-20260630.xsd#ngs_ChiefExecutiveOfficerChiefOperatingOfficerAndChiefFinancialOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019e471f-088b-72eb-952e-0ac7a80b794e" xlink:to="loc_ngs_ChiefExecutiveOfficerChiefOperatingOfficerAndChiefFinancialOfficerMember_019e471f-088b-7058-8771-2a25e5816b36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_ChiefExecutiveOfficerAndChiefOperatingOfficerMember_019e471f-088b-787f-9b24-33a5e09d3e13" xlink:href="ngs-20260630.xsd#ngs_ChiefExecutiveOfficerAndChiefOperatingOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019e471f-088b-72eb-952e-0ac7a80b794e" xlink:to="loc_ngs_ChiefExecutiveOfficerAndChiefOperatingOfficerMember_019e471f-088b-787f-9b24-33a5e09d3e13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e471f-088b-7836-a39a-7dc49e8b2429" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-73cb-8c5b-2722a6cd24ce" xlink:to="loc_srt_RangeAxis_019e471f-088b-7836-a39a-7dc49e8b2429" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e471f-088b-7836-a39a-7dc49e8b2429_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019e471f-088b-7836-a39a-7dc49e8b2429" xlink:to="loc_srt_RangeMember_019e471f-088b-7836-a39a-7dc49e8b2429_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e471f-088b-7df1-93ce-127322d234a9" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019e471f-088b-7836-a39a-7dc49e8b2429" xlink:to="loc_srt_RangeMember_019e471f-088b-7df1-93ce-127322d234a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e471f-088b-7cfc-9ca9-cf37ae5ab055" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e471f-088b-7df1-93ce-127322d234a9" xlink:to="loc_srt_MinimumMember_019e471f-088b-7cfc-9ca9-cf37ae5ab055" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e471f-088b-7df0-85bd-97714019ec26" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e471f-088b-7df1-93ce-127322d234a9" xlink:to="loc_srt_MaximumMember_019e471f-088b-7df0-85bd-97714019ec26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019e471f-088b-793b-a2ef-e8b6504a1230" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-7acd-b922-2c83e0242fa6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019e471f-088b-793b-a2ef-e8b6504a1230" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019e471f-088b-7e15-b9a3-477312a0e74b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-7acd-b922-2c83e0242fa6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019e471f-088b-7e15-b9a3-477312a0e74b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019e471f-088b-77ba-b62e-64be8e6dbaf5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-7acd-b922-2c83e0242fa6" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019e471f-088b-77ba-b62e-64be8e6dbaf5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019e471f-088b-7db2-bc76-83b6ee749eb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-7acd-b922-2c83e0242fa6" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019e471f-088b-7db2-bc76-83b6ee749eb3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_019e471f-088b-7968-8bd6-c2cb692479ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-7acd-b922-2c83e0242fa6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_019e471f-088b-7968-8bd6-c2cb692479ae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_019e471f-088b-768d-8568-a78358f32c64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-7acd-b922-2c83e0242fa6" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_019e471f-088b-768d-8568-a78358f32c64" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/StockBasedandOtherLongTermIncentiveCompensationScheduleofStockBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#StockBasedandOtherLongTermIncentiveCompensationScheduleofStockBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/StockBasedandOtherLongTermIncentiveCompensationScheduleofStockBasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e471f-088b-7031-86b2-5169f46e8c0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e471f-088b-787a-8f5a-5cc292388aec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e471f-088b-7031-86b2-5169f46e8c0c" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e471f-088b-787a-8f5a-5cc292388aec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e471f-088b-7f33-b267-1c097e6f5cd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019e471f-088b-787a-8f5a-5cc292388aec" xlink:to="loc_us-gaap_AwardTypeAxis_019e471f-088b-7f33-b267-1c097e6f5cd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-7f33-b267-1c097e6f5cd2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019e471f-088b-7f33-b267-1c097e6f5cd2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-7f33-b267-1c097e6f5cd2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-77f2-8617-81bcdfc3d852" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019e471f-088b-7f33-b267-1c097e6f5cd2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-77f2-8617-81bcdfc3d852" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_EquityClassifiedAwardsMember_019e471f-088b-7974-8876-4dee429b7ff2" xlink:href="ngs-20260630.xsd#ngs_EquityClassifiedAwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-77f2-8617-81bcdfc3d852" xlink:to="loc_ngs_EquityClassifiedAwardsMember_019e471f-088b-7974-8876-4dee429b7ff2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_LiabilityClassifiedAwardsMember_019e471f-088b-70d0-9214-741c784e76ad" xlink:href="ngs-20260630.xsd#ngs_LiabilityClassifiedAwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-77f2-8617-81bcdfc3d852" xlink:to="loc_ngs_LiabilityClassifiedAwardsMember_019e471f-088b-70d0-9214-741c784e76ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e471f-088b-76b0-b036-382947867d90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019e471f-088b-7031-86b2-5169f46e8c0c" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019e471f-088b-76b0-b036-382947867d90" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/StockBasedandOtherLongTermIncentiveCompensationScheduleofStockOptionsOutstandingDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#StockBasedandOtherLongTermIncentiveCompensationScheduleofStockOptionsOutstandingDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/StockBasedandOtherLongTermIncentiveCompensationScheduleofStockOptionsOutstandingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e471f-088b-72e7-b6ea-ab5a50546d1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_019e471f-088b-71fb-a9f0-abe8ae5632eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e471f-088b-72e7-b6ea-ab5a50546d1d" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_019e471f-088b-71fb-a9f0-abe8ae5632eb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_019e471f-088b-73da-a1fa-05c4766747e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_019e471f-088b-71fb-a9f0-abe8ae5632eb" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_019e471f-088b-73da-a1fa-05c4766747e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e471f-088b-73da-a1fa-05c4766747e4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_019e471f-088b-73da-a1fa-05c4766747e4" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e471f-088b-73da-a1fa-05c4766747e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e471f-088b-7e0b-bac9-5b2d657f99f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_019e471f-088b-73da-a1fa-05c4766747e4" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e471f-088b-7e0b-bac9-5b2d657f99f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RangeOneMember_019e471f-088b-7b56-b5c9-554a97a7d471" xlink:href="ngs-20260630.xsd#ngs_RangeOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e471f-088b-7e0b-bac9-5b2d657f99f3" xlink:to="loc_ngs_RangeOneMember_019e471f-088b-7b56-b5c9-554a97a7d471" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RangeTwoMember_019e471f-088b-7933-a48c-08906e8bb6e9" xlink:href="ngs-20260630.xsd#ngs_RangeTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e471f-088b-7e0b-bac9-5b2d657f99f3" xlink:to="loc_ngs_RangeTwoMember_019e471f-088b-7933-a48c-08906e8bb6e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RangeThreeMember_019e471f-088b-70ce-b0e0-7b34fc9fa32d" xlink:href="ngs-20260630.xsd#ngs_RangeThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_019e471f-088b-7e0b-bac9-5b2d657f99f3" xlink:to="loc_ngs_RangeThreeMember_019e471f-088b-70ce-b0e0-7b34fc9fa32d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_019e471f-088b-78f8-aa94-594fc166e19c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e471f-088b-72e7-b6ea-ab5a50546d1d" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_019e471f-088b-78f8-aa94-594fc166e19c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_019e471f-088b-7590-bdf0-17409e8d790f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e471f-088b-72e7-b6ea-ab5a50546d1d" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_019e471f-088b-7590-bdf0-17409e8d790f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_019e471f-088b-7a0c-9eb6-ca0fa554c477" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e471f-088b-72e7-b6ea-ab5a50546d1d" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_019e471f-088b-7a0c-9eb6-ca0fa554c477" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_019e471f-088b-75f8-8579-1a244577c831" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e471f-088b-72e7-b6ea-ab5a50546d1d" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_019e471f-088b-75f8-8579-1a244577c831" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1_019e471f-088b-70fc-abf1-8a6348334ddd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e471f-088b-72e7-b6ea-ab5a50546d1d" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1_019e471f-088b-70fc-abf1-8a6348334ddd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions_019e471f-088b-72f3-a53f-6b286478177c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e471f-088b-72e7-b6ea-ab5a50546d1d" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions_019e471f-088b-72f3-a53f-6b286478177c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1_019e471f-088b-75fd-94fe-157932760242" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_019e471f-088b-72e7-b6ea-ab5a50546d1d" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1_019e471f-088b-75fd-94fe-157932760242" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/StockBasedandOtherLongTermIncentiveCompensationRestrictedStockActivityCashSettledRSUsandPerformanceShareUnitsDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#StockBasedandOtherLongTermIncentiveCompensationRestrictedStockActivityCashSettledRSUsandPerformanceShareUnitsDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/StockBasedandOtherLongTermIncentiveCompensationRestrictedStockActivityCashSettledRSUsandPerformanceShareUnitsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-78c1-a151-4051e2dd3ec8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-7414-9500-94bf6d414a81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-78c1-a151-4051e2dd3ec8" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-7414-9500-94bf6d414a81" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e471f-088b-791d-814a-d98f0849c85f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-7414-9500-94bf6d414a81" xlink:to="loc_us-gaap_AwardTypeAxis_019e471f-088b-791d-814a-d98f0849c85f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-791d-814a-d98f0849c85f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019e471f-088b-791d-814a-d98f0849c85f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-791d-814a-d98f0849c85f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-79f9-ba56-d20635be817d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019e471f-088b-791d-814a-d98f0849c85f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-79f9-ba56-d20635be817d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_019e471f-088b-704e-801a-fa00107abe7a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-79f9-ba56-d20635be817d" xlink:to="loc_us-gaap_RestrictedStockMember_019e471f-088b-704e-801a-fa00107abe7a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019e471f-088b-72b9-bd66-471e37f26016" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-79f9-ba56-d20635be817d" xlink:to="loc_us-gaap_PerformanceSharesMember_019e471f-088b-72b9-bd66-471e37f26016" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_019e471f-088b-707d-bf08-3b11e645a62b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-7414-9500-94bf6d414a81" xlink:to="loc_us-gaap_VestingAxis_019e471f-088b-707d-bf08-3b11e645a62b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019e471f-088b-707d-bf08-3b11e645a62b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_019e471f-088b-707d-bf08-3b11e645a62b" xlink:to="loc_us-gaap_VestingDomain_019e471f-088b-707d-bf08-3b11e645a62b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019e471f-088b-79e9-a569-738f67a1e002" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_019e471f-088b-707d-bf08-3b11e645a62b" xlink:to="loc_us-gaap_VestingDomain_019e471f-088b-79e9-a569-738f67a1e002" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_CashSettledRSUsMember_019e471f-088b-717d-800a-48894aa3c1fc" xlink:href="ngs-20260630.xsd#ngs_CashSettledRSUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019e471f-088b-79e9-a569-738f67a1e002" xlink:to="loc_ngs_CashSettledRSUsMember_019e471f-088b-717d-800a-48894aa3c1fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e471f-088b-7028-b68f-f1d52d168975" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-78c1-a151-4051e2dd3ec8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e471f-088b-7028-b68f-f1d52d168975" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e471f-088b-7eeb-a5c2-b0fcaf86ea23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e471f-088b-7028-b68f-f1d52d168975" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e471f-088b-7eeb-a5c2-b0fcaf86ea23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019e471f-088b-7feb-b8e8-c134b08f728e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e471f-088b-7028-b68f-f1d52d168975" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019e471f-088b-7feb-b8e8-c134b08f728e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019e471f-088b-7893-b4d6-ac4c819443c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e471f-088b-7028-b68f-f1d52d168975" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019e471f-088b-7893-b4d6-ac4c819443c1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019e471f-088b-7e3e-9fcb-b42cae08e1d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019e471f-088b-7028-b68f-f1d52d168975" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019e471f-088b-7e3e-9fcb-b42cae08e1d9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019e471f-088b-7d90-b348-48eb1007d531" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e471f-088b-7be4-94f1-25d044047b9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-78c1-a151-4051e2dd3ec8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e471f-088b-7be4-94f1-25d044047b9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e471f-088b-7351-8393-5c818e8df45f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e471f-088b-7be4-94f1-25d044047b9f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e471f-088b-7351-8393-5c818e8df45f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019e471f-088b-7605-8f07-c87938c53a15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e471f-088b-7be4-94f1-25d044047b9f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019e471f-088b-7605-8f07-c87938c53a15" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019e471f-088b-7543-958d-a6ba206291e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e471f-088b-7be4-94f1-25d044047b9f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019e471f-088b-7543-958d-a6ba206291e6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019e471f-088b-7ac4-992f-9c3fa084ebec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019e471f-088b-7be4-94f1-25d044047b9f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019e471f-088b-7ac4-992f-9c3fa084ebec" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019e471f-088b-71a6-8542-059c4967b60a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndSettledInCash_019f6595-af7c-71ec-bc82-ff1fac64b89c" xlink:href="ngs-20260630.xsd#ngs_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndSettledInCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-78c1-a151-4051e2dd3ec8" xlink:to="loc_ngs_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndSettledInCash_019f6595-af7c-71ec-bc82-ff1fac64b89c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsRemainingVestedSharesSettled_019f6595-af7d-7186-9df6-2cb25dc4d4ff" xlink:href="ngs-20260630.xsd#ngs_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsRemainingVestedSharesSettled"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-78c1-a151-4051e2dd3ec8" xlink:to="loc_ngs_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsRemainingVestedSharesSettled_019f6595-af7d-7186-9df6-2cb25dc4d4ff" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/StockBasedandOtherLongTermIncentiveCompensationValuationAssumptionsDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#StockBasedandOtherLongTermIncentiveCompensationValuationAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/StockBasedandOtherLongTermIncentiveCompensationValuationAssumptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-74d2-8175-6b8928ad89c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-700f-a193-116b129521f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-74d2-8175-6b8928ad89c9" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-700f-a193-116b129521f9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019e471f-088b-7678-a66e-a772215537dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019e471f-088b-700f-a193-116b129521f9" xlink:to="loc_us-gaap_AwardTypeAxis_019e471f-088b-7678-a66e-a772215537dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-7678-a66e-a772215537dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019e471f-088b-7678-a66e-a772215537dc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-7678-a66e-a772215537dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-7d32-8ca0-78dcc880a3d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019e471f-088b-7678-a66e-a772215537dc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-7d32-8ca0-78dcc880a3d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019e471f-088b-7706-83e9-dffd4896e367" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019e471f-088b-7d32-8ca0-78dcc880a3d2" xlink:to="loc_us-gaap_PerformanceSharesMember_019e471f-088b-7706-83e9-dffd4896e367" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019e471f-088b-7ccc-b5dc-30b1ac6700b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-74d2-8175-6b8928ad89c9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019e471f-088b-7ccc-b5dc-30b1ac6700b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_019f63a1-5b92-73c5-bab2-a8481cc0f3dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-74d2-8175-6b8928ad89c9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_019f63a1-5b92-73c5-bab2-a8481cc0f3dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_019f63a1-5b92-7d52-8393-6a9decd13091" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-74d2-8175-6b8928ad89c9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_019f63a1-5b92-7d52-8393-6a9decd13091" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_019f63a0-4014-70df-b1d5-4caa819c690d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-74d2-8175-6b8928ad89c9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_019f63a0-4014-70df-b1d5-4caa819c690d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_019f63a0-874b-7211-910a-4fc6a206d77c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019e471f-088b-74d2-8175-6b8928ad89c9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_019f63a0-874b-7211-910a-4fc6a206d77c" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/EarningsperShareScheduleofDeterminationofDilutedEarningsPerShareDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#EarningsperShareScheduleofDeterminationofDilutedEarningsPerShareDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/EarningsperShareScheduleofDeterminationofDilutedEarningsPerShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019e471f-088b-79b7-bd77-e260cf57e198" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019e471f-088b-768d-b680-4bc1e3bf1fb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019e471f-088b-79b7-bd77-e260cf57e198" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019e471f-088b-768d-b680-4bc1e3bf1fb3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e471f-088b-77ca-8ac8-a0850b065e88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019e471f-088b-768d-b680-4bc1e3bf1fb3" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e471f-088b-77ca-8ac8-a0850b065e88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e471f-088b-77ca-8ac8-a0850b065e88_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e471f-088b-77ca-8ac8-a0850b065e88" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e471f-088b-77ca-8ac8-a0850b065e88_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e471f-088b-7215-b344-c39cf54e4cef" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019e471f-088b-77ca-8ac8-a0850b065e88" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e471f-088b-7215-b344-c39cf54e4cef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019e471f-088b-75be-81c6-ecebfd8335e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e471f-088b-7215-b344-c39cf54e4cef" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019e471f-088b-75be-81c6-ecebfd8335e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ngs_RestrictedStockAndRestrictedStockUnitsMember_019e471f-088b-7ae6-82e6-1996880799e5" xlink:href="ngs-20260630.xsd#ngs_RestrictedStockAndRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e471f-088b-7215-b344-c39cf54e4cef" xlink:to="loc_ngs_RestrictedStockAndRestrictedStockUnitsMember_019e471f-088b-7ae6-82e6-1996880799e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019e471f-088b-7973-ac8c-bade6708736c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019e471f-088b-7215-b344-c39cf54e4cef" xlink:to="loc_us-gaap_PerformanceSharesMember_019e471f-088b-7973-ac8c-bade6708736c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019e471f-088b-7f21-8fa5-fb06c99863ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019e471f-088b-79b7-bd77-e260cf57e198" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019e471f-088b-7f21-8fa5-fb06c99863ab" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.ngsgi.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="ngs-20260630.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://www.ngsgi.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_019e471f-088b-790c-8c02-926d9abb1b9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_019e471f-088b-72e3-ae68-72334de7a20b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_019e471f-088b-790c-8c02-926d9abb1b9e" xlink:to="loc_us-gaap_SubsequentEventTable_019e471f-088b-72e3-ae68-72334de7a20b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019e471f-088b-75ff-8879-091e163a03d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019e471f-088b-72e3-ae68-72334de7a20b" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019e471f-088b-75ff-8879-091e163a03d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019e471f-088b-75ff-8879-091e163a03d1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019e471f-088b-75ff-8879-091e163a03d1" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019e471f-088b-75ff-8879-091e163a03d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019e471f-088b-7729-b4e2-2eb7584cfefe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019e471f-088b-75ff-8879-091e163a03d1" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019e471f-088b-7729-b4e2-2eb7584cfefe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019e471f-088b-7c86-bade-23be7e1a4b90" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019e471f-088b-7729-b4e2-2eb7584cfefe" xlink:to="loc_us-gaap_SubsequentEventMember_019e471f-088b-7c86-bade-23be7e1a4b90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_019e471f-088b-7f80-9c3c-809b4d17fbac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019e471f-088b-790c-8c02-926d9abb1b9e" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_019e471f-088b-7f80-9c3c-809b4d17fbac" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
