13.    Unit-Based Compensation 

During the three months ended March 31, 2026 and 2025, the Partnership granted service, performance and market-based awards under its 2017 Long-Term Incentive Plan. The Partnership's service and performance-based awards are valued using the closing price of NRP's common units as of the grant date while the Partnership's market-based awards are valued using a Monte Carlo simulation. The grant date fair value of the awards granted during the three months ended March 31, 2026 and 2025 was $8.6 million and $6.8 million, respectively, which included a grant date fair value of $3.1 million and $2.5 million for the market-based awards valued using a Monte Carlo simulation during the three months ended March 31, 2026 and 2025, respectively. Total unit-based compensation expense associated with service, performance and market-based awards was $1.2 million and $2.7 million for the three months ended March 31, 2026 and 2025, respectively, and is included in general and administrative expenses and operating and maintenance expenses on the Partnership's Consolidated Statements of Comprehensive Income. The unamortized cost associated with unvested outstanding awards as of March 31, 2026 was $11.9 million, which will be recognized over a weighted average period of 2.3 years. The unamortized cost associated with unvested outstanding awards as of  December 31, 2025 was $5.9 million. The Partnership paid $8.9 million and $5.5 million in cash during the three months ended  March 31, 2026 and 2025, respectively, for taxes on the unit-based award settlements during the respective years. These cash payments are included in other items, net under cash flows from financing activities on the Partnership's Consolidated Statements of Cash Flows. 

A summary of the unit activity in the outstanding grants during 2026 is as follows: