Exhibit 99.1

Okeanis Eco Tankers Corp. Reports Financial Results for the First Quarter of 2026

ATHENS, GREECE, May 13, 2026 – Okeanis Eco Tankers Corp. (together with its subsidiaries, unless context otherwise dictates, “OET” or the “Company”) (NYSE: ECO, OSE: OET) today reported its unaudited condensed financial results for the first quarter of 2026, which are attached to this press release.

Financial performance of the First Quarter Ended March 31, 2026

Alternative performance metrics and market development

Declaration of Q1 2026 dividend

The Company’s board of directors declared a dividend of $2.00 per common share to shareholders. Dividends payable to common shares registered in the Euronext VPS will be distributed in NOK. The cash payment will be paid on June 5, 2026, to shareholders of record as of May 28, 2026. The common shares will be traded ex-dividend on the NYSE as from and including May 28, 2026, and the common shares will be traded ex-dividend on the Oslo Stock Exchange as from and including May 27, 2026. Due to the implementation of the Central Securities Depository Regulation (CSDR) in Norway, dividends payable on common shares registered with Euronext VPS are expected to be distributed to Euronext VPS shareholders on or about June 10, 2026.

*The Company uses certain financial information calculated on a basis other than in accordance with generally accepted accounting principles and International Financial Reporting Standards (“IFRS”), including TCE, Daily TCE, EBITDA, Adjusted EBITDA, Adjusted profit, Adjusted earnings per share, and Daily Opex. For a reconciliation of these non-IFRS measures, please refer to the end of this press release.

Presentation

OET will be hosting a conference call and webcast at 14:30 CET on Thursday, May 14, 2026 to discuss the Q1 2026 results.

The webcast will include a slide presentation and will be available on the following link: https://events.q4inc.com/attendee/446194895

An audio replay of the conference call will be available on our website: http://www.okeanisecotankers.com/reports/

Contacts

Company:

Iraklis Sbarounis, CFO

Tel: +30 210 480 4200

ir@okeanisecotankers.com

Investor Relations / Media Contact:

Nicolas Bornozis, President

Capital Link, Inc.

230 Park Avenue, Suite 1540, New York, N.Y. 10169

Tel: +1 (212) 661-7566

okeanisecotankers@capitallink.com

About OET

OET is a leading international tanker company providing seaborne transportation of crude oil and refined products. The Company was incorporated on April 30, 2018 under the laws of the Republic of the Marshall Islands and is listed on Oslo Stock Exchange under the symbol OET and the New York Stock Exchange under the symbol ECO. The sailing fleet consists of eight modern scrubber-fitted Suezmax tankers and eight modern scrubber-fitted VLCC tankers.

Forward Looking Statements

This communication contains “forward-looking statements”, including as defined under U.S. federal securities laws. Forward-looking statements provide the Company’s current expectations or forecasts of future events. Forward-looking statements include statements about the Company’s expectations, beliefs, plans, objectives, intentions, assumptions and other statements that are not historical facts or that are not present facts or conditions. Words or phrases such as “anticipate,” “believe,” “continue,” “estimate,” “expect,” “hope,” “intend,” “may,” “ongoing,” “plan,” “potential,” “predict,” “project,” “should,” “will” or similar words or phrases, or the negatives of those words or phrases, may identify forward-looking statements, but the absence of these words does not necessarily mean that a statement is not forward-looking. Forward-looking statements are subject to known and unknown risks and uncertainties and are based on potentially inaccurate assumptions that could cause actual results to differ materially from those expected or implied by the forward-looking statements. The Company’s actual results could differ materially from those anticipated in forward-looking statements for many reasons, including as described in the Company’s filings with the U.S. Securities and Exchange Commission (the “SEC”). Accordingly, you should not unduly rely on these forward-looking statements, which speak only as of the date of this communication. Factors that could cause actual results to differ materially include, but are not limited to, the Company’s operating or financial results; the Company’s liquidity, including its ability to service its indebtedness; competitive factors in the market in which the Company operates; shipping industry trends, including charter rates, vessel values and factors affecting vessel supply and demand; future, pending or recent acquisitions and dispositions, business strategy, areas of possible expansion or contraction, and expected capital spending or operating expenses; risks associated with operations; broader market impacts arising from war (or threatened war) or international hostilities; risks associated with pandemics, including effects on demand for oil and other products transported by tankers and the transportation thereof; and other factors listed from time to time in the Company’s filings with the SEC. Except to the extent required by law, the Company expressly disclaims any obligations or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in the Company’s expectations with respect thereto or any change in events, conditions, or circumstances on which any statement is based. You should, however, review the factors and risks the Company describes in the reports it files and furnishes from time to time with the SEC, which can be obtained free of charge on the SEC’s website at www.sec.gov.

This information is subject to the disclosure requirements pursuant to Section 5-12 of the Norwegian Securities Trading Act.

Okeanis Eco Tankers Corp. Reports Financial Results for the First Quarter of 2026

ATHENS, GREECE, May 13, 2026 – Okeanis Eco Tankers Corp. (together with its subsidiaries, unless context otherwise dictates, “OET” or the “Company”) (NYSE: ECO, OSE: OET) today reported its unaudited condensed financial results for the first quarter of 2026.

Financial performance of the First Quarter Ended March 31, 2026

Alternative performance metrics and market development

Declaration of Q1 2026 dividend

The Company’s board of directors declared a dividend of $2.00 per common share to shareholders. Dividends payable to common shares registered in the Euronext VPS will be distributed in NOK. The cash payment will be paid on June 5, 2026, to shareholders of record as of May 28, 2026. The common shares will be traded ex-dividend on the NYSE as from and including May 28, 2026, and the common shares will be traded ex-dividend on the Oslo Stock Exchange as from and including May 27, 2026. Due to the implementation of the Central Securities Depository Regulation (CSDR) in Norway, dividends payable on common shares registered with Euronext VPS are expected to be distributed to Euronext VPS shareholders on or about June 10, 2026.

Financial results overview-first quarter of 2026

*The Company uses certain financial information calculated on a basis other than in accordance with generally accepted accounting principles and International Financial Reporting Standards (“IFRS”), including TCE, Daily TCE, EBITDA, Adjusted EBITDA, Adjusted profit, Adjusted earnings per share, and Daily Opex. For a reconciliation of these non-IFRS measures, please refer to the end of this press release.

**Out of the total cash balance, $45.0 million is classified as restricted, representing short term (less than three months) cash collateral held in a restricted account in connection with Nissos Piperi facility. The Nissos Piperi Facility, for the duration of such cash collateral, bears interest at a reduced interest all-in rate of 0.5%.

***Book Leverage is calculated as net debt over net debt plus equity.

Key information, management commentary and subsequent events

Fleet*

As of March 31, 2026, the Company’s fleet was comprised of the following 16 vessels with an average age of 5.8 years and aggregate capacity of approximately 3.8 million deadweight tons:

*Age and deadweight capacity do not include the Suezmax vessels that are expected to be delivered in May and July of 2026.

Presentation

OET will be hosting a conference call and webcast at 14:30 CET on Thursday, May 14, 2026 to discuss the Q1 2026 results.

The webcast will include a slide presentation and will be available on the following link: https://events.q4inc.com/attendee/446194895

An audio replay of the conference call will be available on our website: http://www.okeanisecotankers.com/reports/

Unaudited condensed consolidated statements of profit or loss and other comprehensive income

Unaudited condensed consolidated statements of financial position

Unaudited condensed consolidated statement of changes in shareholders’ equity

Unaudited condensed consolidated statements of cash flows

USE AND RECONCILIATION OF ALTERNATIVE PERFORMANCE MEASURES

The Company together with its wholly owned subsidiaries, (the “Group”) evaluates its vessels’ operations and financial results principally by assessing their revenue generation (and not by the type of vessel, employment, customer, or type of charter). Among others, TCE, Daily TCE rate, EBITDA, Adjusted EBITDA, Daily Opex, Adjusted Profit/(loss), and Adjusted Earnings/(loss) per share are used as key performance indicators.

Daily TCE rate

In the shipping industry, economic decisions are based on vessels’ deployment upon anticipated TCE rates and time charter equivalent revenue, and industry analysts typically measure shipping freight rates in terms of TCE rates. This is because under time-charter and bareboat contracts the customer usually pays the voyage expenses, while under voyage charters the ship-owner usually pays the voyage expenses, which typically are added to the hire rate at an approximate cost. In a voyage charter contract, consideration is received for the use of a vessel between designated ports for the duration of the voyage only, at an agreed upon rate per volume of cargo carried. In a time charter contract, the customer (also known as the charterer) is responsible to pay for fuel consumed and port expenses incurred during the agreed period of time. In a voyage charter contract, the Company is responsible for maintaining the voyage, including vessel scheduling and routing, as well as any related voyage expenses, such as fuel, port and other expenses. Under voyage charters, the majority of voyage expenses are generally borne by us whereas for vessels in a time charter, such expenses are borne by the time charter operator. In a bareboat charter, the customer pays for all of the vessel’s operating expenses, and undertakes to maintain the vessel in a good state of repair and efficient operating condition and drydock the vessel during this period as per the classification society requirements. We may incur voyage related expenses when positioning or repositioning vessels before or after the period of a time or other charter, during periods of commercial waiting time or while off-hire during drydocking or due to other unforeseen circumstances. Because of the different nature of these types of arrangements, the amount of revenues earned by the Company can differ significantly between them.

The Daily Time Charter Equivalent Rate (“TCE rate”) is a measure of the average daily revenue performance of a vessel. The TCE rate and time charter equivalent revenue (TCE) are not measures of revenue under generally accepted accounting principles (i.e., they are non-GAAP measures) or IFRS and should not be considered as an alternative to any measure of revenue and financial performance presented in accordance with IFRS. We calculate the TCE rate by dividing revenues (time charter and/or voyage charter revenues), less commission and voyage expenses (which then equals “time charter equivalent revenue”), by the number of operating days (we define operating days as calendar days less any scheduled or unscheduled days that our vessels are off-hire due to unforeseen technical and commercial circumstances) during that period. Our calculation of the TCE rate and time charter equivalent revenue may not be comparable to that reported by other companies. We define calendar days as the total number of days the vessels were in our possession for the relevant period. Calendar days are an indicator of the size of our fleet during the relevant period and affect the amount of expenses that we record during that period. We and other companies in the shipping industry use operating days to measure the aggregate number of days in a period that our vessels generate revenues. The period a vessel is not being chartered or is unable to perform the services for which it is required under a charter is “off-hire”.

We use the TCE rate and time charter equivalent revenue because they provide a means of comparison between different types of vessel employment and, therefore, assists our decision-making process with regards to the operation and use of our vessels and in evaluating our financial performance. We believe the TCE rate and time charter equivalent revenue provide additional meaningful information to our investors, constituting a comparison to Revenue, the most directly comparable GAAP and IFRS measure, that also enables our management to evaluate the performance and deployment of our fleet and in evaluating their financial performance. The TCE rate and time charter equivalent revenue are measures used to compare period-to-period changes in a company’s performance, and management believes that the TCE rate and time charter equivalent revenue provide meaningful information to our investors.

The following table sets forth our computation of TCE rates, including a reconciliation of revenues to the TCE rates (unaudited) for the periods presented:

Daily Opex

Daily Opex per vessel is an alternative performance measure that provides meaningful information to our management with regards to our vessels’ efficiency and deployment. Daily Opex is not a measure under generally accepted accounting principles (i.e., it is a non-GAAP measure) or IFRS and should not be considered as an alternative to any measure of expenses and financial performance presented in accordance with IFRS. Our reconciliation of daily Opex, including management fees, may deviate from that reported by other companies. We believe Daily Opex provides additional meaningful information in conjunction with Vessel operating expenses, the most directly comparable GAAP and IFRS measure, because it provides meaningful information to our investors in evaluating our financial performance. Also, it is an alternative measure that provides meaningful information to our management with regards to our vessels’ efficiency and deployment.

Daily Opex is calculated as vessel operating expenses and technical management fees divided by calendar days, for the relevant periods.

The following table sets forth our reconciliation of daily Opex (unaudited) for the periods presented:

EBITDA, Adjusted EBITDA, Adjusted Profit and Adjusted Earnings per share

Earnings before interest, tax, depreciation and amortization (EBITDA) is an alternative performance measure, derived directly from the statement of profit or loss and other comprehensive income by adding back to profit/(loss) depreciation, amortization, interest and finance costs and subtracting interest income. Adjusted EBITDA is defined as EBITDA before non-recurring items, unrealized losses/(gains) on derivatives, realized losses/(gains) on derivatives, foreign exchange (gains)/losses, (gain)/loss from loan modifications and loss on debt extinguishment. Adjusted profit/(loss) is defined as reported profit/(loss) before non-recurring items, unrealized losses/(gains) on derivatives, impairment loss, loan modification gain/(loss), loss on debt extinguishment and gain/(loss) on disposal of vessels, if any. Adjusted earnings/(loss) per share is defined as adjusted profit/(loss) divided by the weighted average number of common shares outstanding in the period.

Furthermore, EBITDA, Adjusted EBITDA, Adjusted profit/(loss) and Adjusted earnings/(loss) per share have certain limitations in use and should not be considered alternatives to reported profit/(loss), operating profit, cash flows from operations, earnings per share or any other GAAP or IFRS measure of financial performance. EBITDA, Adjusted EBITDA, Adjusted profit/(loss) and Adjusted earnings/(loss) per share exclude some, but not all, items that affect profit/(loss).

EBITDA, Adjusted EBITDA, Adjusted Profit and Adjusted Earnings per share are not measures of profit under generally accepted accounting principles (i.e., they are non-GAAP measures) or IFRS and should not be considered as an alternative to any measure of revenue and financial performance presented in accordance with IFRS. EBITDA, Adjusted EBITDA, Adjusted profit and Adjusted earnings per share are used as supplemental financial measures by management and external users of financial statements to assess our operating performance. We believe that EBITDA, Adjusted EBITDA, Adjusted profit and Adjusted earnings per share assist our management and our investors by providing useful information that increases the comparability of our operating performance from period to period and against our previous performance and the operating performance of other companies in our industry that provide relevant information. We believe EBITDA, Adjusted EBITDA, Adjusted profit and Adjusted earnings per share provide additional meaningful information in conjunction with profit, the most directly comparable GAAP and IFRS measure, because they provide meaningful information in evaluating our financial performance.

Our method of computing EBITDA, Adjusted EBITDA, Adjusted profit/(loss) and Adjusted earnings/(loss) per share may not be consistent with similarly titled measures of other companies and, therefore, might not be comparable with other companies.

The following table sets forth a reconciliation of profit to EBITDA (unaudited) and Adjusted EBITDA (unaudited) for the periods presented:

The following table sets forth a reconciliation of profit to Adjusted profit (unaudited) and a computation of Adjusted earnings per share (unaudited) for the periods presented:

Forward Looking Statements

This communication contains “forward-looking statements”, including as defined under U.S. federal securities laws. Forward-looking statements provide the Company’s current expectations or forecasts of future events. Forward-looking statements include statements about the Company’s expectations, beliefs, plans, objectives, intentions, assumptions and other statements that are not historical facts or that are not present facts or conditions. Words or phrases such as “anticipate,” “believe,” “continue,” “estimate,” “expect,” “hope,” “intend,” “may,” “ongoing,” “plan,” “potential,” “predict,” “project,” “should,” “will” or similar words or phrases, or the negatives of those words or phrases, may identify forward-looking statements, but the absence of these words does not necessarily mean that a statement is not forward-looking. Forward-looking statements are subject to known and unknown risks and uncertainties and are based on potentially inaccurate assumptions that could cause actual results to differ materially from those expected or implied by the forward-looking statements. The Company’s actual results could differ materially from those anticipated in forward-looking statements for many reasons, including as described in the Company’s filings with the U.S. Securities and Exchange Commission (the “SEC”). Accordingly, you should not unduly rely on these forward-looking statements, which speak only as of the date of this communication. Factors that could cause actual results to differ materially include, but are not limited to, the Company’s operating or financial results; the Company’s liquidity, including its ability to service its indebtedness; competitive factors in the market in which the Company operates; shipping industry trends, including charter rates, vessel values and factors affecting vessel supply and demand; future, pending or recent acquisitions and dispositions, business strategy, areas of possible expansion or contraction, and expected capital spending or operating expenses; risks associated with operations; broader market impacts arising from war (or threatened war) or international hostilities; risks associated with pandemics, including effects on demand for oil and other products transported by tankers and the transportation thereof; and other factors listed from time to time in the Company’s filings with the SEC. Except to the extent required by law, the Company expressly disclaims any obligations or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in the Company’s expectations with respect thereto or any change in events, conditions, or circumstances on which any statement is based. You should, however, review the factors and risks the Company describes in the reports it files and furnishes from time to time with the SEC, which can be obtained free of charge on the SEC’s website at www.sec.gov.