POLL RESULTS OF THE 2023 ANNUAL GENERAL MEETING

Hong Kong Exchanges and Clearing Limited and The Stock Exchange of Hong Kong Limited take no responsibility for the contents of this announcement make no representation as to its accuracy or completeness and expressly disclaim any liability whatsoever for any loss howsoever arising from or in reliance upon the whole or any part of the contents of this announcement.(Incorporated in Hong Kong with limited liability under the Companies Ordinance) Stock Codes: 00883 (HKD counter) and 80883 (RMB counter) POLL RESULTS OF THE 2023 ANNUAL GENERAL MEETING References are made to the notice (the “Notice”) and the circular (the “Circular”) of the annual general meeting (the “Annual General Meeting”) of CNOOC Limited (the “Company”) dated 14 May 2024. Unless otherwise defined in this announcement terms used herein shall have the same meanings as those defined in the Notice and the Circular.I. CONVENING AND ATTENDANCE OF THE ANNUAL GENERAL MEETING The Company held the Annual General Meeting on Friday 7 June 2024 at 2:00 p.m. at JW Marriott Hotel Hong Kong Pacific Place 88 Queensway Hong Kong. 1. Total number of Shareholders and proxies attending the Annual General 797 Meeting of which number of holders of RMB Shares 272 number of holders of Hong Kong Shares 525 2. Total number of valid voting shares held by the attending Shareholders 32282325565 of which number of shares held by holders of RMB Shares 852258491 number of shares held by holders of Hong Kong Shares 31430067074 3. Percentage of voting shares held by such attending Shareholders as 67.867399 compared with the total voting Shares (%) of which the proportion of shares held by holders of RMB Shares in the 1.791710 total number of voting shares (%) the proportion of shares held by holders of Hong Kong shares in 66.075689 the total number of voting shares (%) As at 4:30 p.m. on Monday 3 June 2024 the total number of shares issued by the Company was 147566763984 which represents the total number of shares entitling the Shareholders to attend and vote on the resolutions at the Annual General Meeting.No Shareholders who are entitled to attend the Annual General Meeting are required to abstain from voting in favour or to abstain from voting according to the Hong Kong Listing Rules.The Annual General Meeting was convened by the Board and chaired by Mr. Wang Dongjin (Chairman of the Board) with a combination of both onsite and online voting. Ms. Wen Dongfen a non-executive Director was unable to attend the Annual General Meeting due to other business arrangement. All the other Directors then in office attended the Annual General Meeting in person.The Joint Company Secretary Mr. Xu Yugao also attended the meeting. The convening of and the procedures for holding the Annual General Meeting and the voting procedures at the Annual General Meeting were in compliance with the relevant requirements of the Articles of Association.II. POLL RESULTS OF THE ANNUAL GENERAL MEETING 1. To receive and consider the audited financial statements independent auditors’ report and the report of the Directors for the year ended 31 December 2023.Results: Approved Voting details: Shareholder For Against Abstain category Number of Number of votes (%) votes (%) Number of votes (%) RMB Shares 852178918 99.990663 6673 0.000783 72900 0.008554 Hong Kong Shares 31425483163 99.985416 100026 0.000318 4483885 0.014266 Total 32277662081 99.985554 106699 0.000331 4556785 0.014115 2. To re-elect Mr. Wang Dongjin as a non-executive Director. Result: Approved Voting details: Shareholder For Against Abstain category Number of Number of Number votes (%) votes (%) of votes (%) RMB Shares 845989542 99.264431 6196049 0.727015 72900 0.008554 2Hong Kong Shares 30743802154 97.816534 681532035 2.168408 4732885 0.015058 Total 31589791696 97.854758 687728084 2.130355 4805785 0.014887 3. To re-elect Mr. Qiu Zhi Zhong as an independent non-executive Director. Result: Approved Voting details: Shareholder For Against Abstain category Number of (%) Number of Numbervotes votes (%) of votes (%) RMB Shares 847602942 99.453740 4582649 0.537706 72900 0.008554 Hong Kong Shares 30845469970 98.140007 579810219 1.844763 4786885 0.015230 Total 31693072912 98.174690 584392868 1.810256 4859785 0.015054 4. To authorise the Board to fix the remuneration of each of the Directors. Result: Approved Voting details: Shareholder For Against Abstain category Number of Number of Number votes (%) votes (%) of votes (%) RMB Shares 852162318 99.988716 6773 0.000794 89400 0.010490 Hong Kong Shares 31425162138 99.984394 104051 0.000331 4800885 0.015275 Total 32277324456 99.984508 110824 0.000344 4890285 0.015148 5. To re-appoint Ernst & Young Hua Ming LLP (Special General Partnership) and Ernst & Young as the domestic and overseas independent auditors of the Company and its subsidiaries for the year of 2024 respectively and to authorise the Board to fix the remuneration of the aforementioned independent auditors. 3Result: Approved Voting details: Shareholder For Against Abstain category Number of Number Number votes (%) of votes (%) of votes (%) RMB Shares 852178918 99.990663 6673 0.000783 72900 0.008554 Hong Kong Shares 31420377161 99.969170 4921028 0.015657 4768885 0.015173 Total 32272556079 99.969737 4927701 0.015265 4841785 0.014998 6. To declare a final dividend for the year ended 31 December 2023. Result: Approved Voting details: Shareholder For Against Abstain category Number of Number Number votes (%) of votes (%) of votes (%) RMB Shares 852179918 99.990781 6673 0.000783 71900 0.008436 Hong Kong Shares 31425193162 99.984493 104026 0.000331 4769886 0.015176 Total 32277373080 99.984659 110699 0.000343 4841786 0.014998 7. To authorise the Board to determine the declaration plan of the 2024 interim dividend within the scope of the Interim Dividend Authorisation and to authorise the Board and the persons authorised by the Board to deal with all matters relating to the declaration of the 2024 interim dividend by the Company.Result: Approved Voting details: Shareholder For Against Abstain category Number of Number Number votes (%) of votes (%) of votes (%) 4RMB Shares 852179918 99.990781 6673 0.000783 71900 0.008436 Hong Kong Shares 31425195163 99.984499 104026 0.000331 4767885 0.015170 Total 32277375081 99.984665 110699 0.000343 4839785 0.014992 8. To grant a general mandate to the Directors to buy back Shares in the capital of the Company not exceeding 10% of the total number of issued Shares as at the date of passing of this resolution and the amount used to buy back RMB Shares shall not exceeding 20% of the audited net profit attributable to equity shareholders of the Company in the latest financial year.* Result: Approved Voting details: Shareholder For Against Abstain category Number of (%) Number (%) Numbervotes of votes of votes (%) RMB Shares 852178118 99.990569 7473 0.000877 72900 0.008554 Hong Kong Shares 31425136163 99.984311 163026 0.000519 4767885 0.015170 Total 32277314281 99.984477 170499 0.000528 4840785 0.014995 9. To grant a general mandate to the Directors to issue allot and deal with additional Shares in the capital of the Company and to make or grant offers agreements options and similar rights to subscribe for or convert any security into shares in the Company which would or might require the exercise of such power which shall not exceed 20% of the total number of issued Shares as at the date of passing of this resolution.* Result: Approved Voting details: Shareholder For Against Abstain category Number of (%) Number of Number ofvotes votes (%) votes (%) RMB Shares 849958643 99.730147 2214948 0.259891 84900 0.009962 5Hong Kong Shares 30297856482 96.397683 1127436707 3.587128 4773885 0.015189 Total 31147815125 96.485661 1129651655 3.499288 4858785 0.015051 10. To extend the general mandate granted to the Directors to issue allot and deal with additional Shares of the Company and to make or grant offers agreements options and similar rights to subscribe for or convert any security into Shares in the Company by the aggregate number of shares bought back which shall not exceed 10% of the total number of issued Shares of the Company as at the date of passing of this resolution.* Result: Approved Voting details: Shareholder For Against Abstain category Number of Number of Number of votes (%) votes (%) votes (%) RMB Shares 849970643 99.731555 2213948 0.259774 73900 0.008671 Hong Kong Shares 30679326123 97.611392 745915066 2.373254 4825885 0.015354 Total 31529296766 97.667365 748129014 2.317457 4899785 0.015178 11. To consider and approve the Proposed Amendments to the Articles of Association the adoption of the amended Articles of Association with immediate effect after the closing of the Annual General Meeting and to authorize any Director or company secretary (secretary to the Board) of the Company to carry out and take all actions necessary and to sign all necessary documents in connection with or to give effect to this special resolution. * Result: Approved Voting details: Shareholder For Against Abstain category Number of (%) Number of Numbervotes votes (%) of votes (%) RMB Shares 848196917 99.523434 3988674 0.468012 72900 0.008554 6Hong Kong Shares 31303094601 99.596016 122178586 0.388731 4793887 0.015253 Total 32151291518 99.594100 126167260 0.390824 4866787 0.015076 * The full text of this resolution is set out in the Notice.Details of the poll results on the resolutions involving significant matters by holders of RMB Shares with less than 5% shareholdings as disclosed pursuant to the relevant rules of the Shanghai Stock Exchange are set out in the Announcement on Resolutions of 2023 Annual General Meeting issued by the Company on the Shanghai Stock Exchange on 8 June 2024.III. THE EXPLANATION ON RESOLUTION VOTING The vote-taking at the Annual General Meeting was counted and scrutinised by Shareholders’ representatives witnessed lawyers and representatives from Hong Kong Registrars Limited. The aforementioned resolutions numbered 1 to 10 are ordinary resolutions and have been passed by more than one half of the total shares with valid voting rights held by the Shareholders or their proxies present at the Annual General Meeting. The aforementioned resolution numbered 11 is a special resolution and has been passed by not less than three-fourths of the total shares with valid voting rights held by the Shareholders or their proxies present at the Annual General Meeting. The Company is pleased to announce that all the resolutions proposed at the Annual General Meeting have been duly passed.By order of the Board CNOOC Limited Xu Yugao Joint Company Secretary Hong Kong 7 June 2024 As at the date of this announcement Non-executive Directors the Board comprises: Wang Dongjin (Chairman) Wen Dongfen Executive Director Independent non-executive Directors Zhou Xinhuai (Vice Chairman) Chiu Sung Hong Qiu Zhi Zhong Lin Boqiang Li Shuk Yin Edwina 7