[FORM 20-F (Mark One) ¨ OR ý For the fiscal year ended December 31, 2013 OR ¨ For the transition period from _________________ to _______________ OR ¨ Date of event requiring this shell company report CNOOC LIMITED N/A Hong Kong (Jurisdiction of incorporation or organization) 65th Floor, Bank of China Tower One Garden Road, Central Hong Kong Hua Zhong th] [China National Offshore Oil Corporation and CNOOC Limited Framework Agreement in respect of the Connected Transactions Table of Contents 1. Scope of Products and Services 2. Transaction Principles 3. Pricing Principles 4. Mode of Operations 5. 6. Term and Termination of the specific Product and Service Contracts 7. 8.] [Subsidiaries As of December 31, 2013, we owned, directly or indirectly, the following subsidiaries. All of these entities are private limited liability companies and they do business in their corporate names. Name of entity Our interest Jurisdiction of incorporation CNOOC China Limited 100% Tianjin, PRC CNOOC International Limited 100% British Virgin Islands China Offshore Oil (Singapore) International Pte Ltd 100%] [CNOOC Limited (incorporated under laws of Hong Kong with limited liability) Code of Ethics for Directors and Senior Officers 20 August 2013 I. INTRODUCTION Each of the directors and Senior Officers has the responsibility to obey the law and act honestly and ethically. To that end, this Code of Ethics is a guide intended to assist each of the directors] [CERTIFICATIONS I, Fanrong Li, certify that: 1. I have reviewed this annual report on Form 20-F of CNOOC Limited; 2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made,] [CERTIFICATIONS I, Hua Zhong, certify that: 1. I have reviewed this annual report on Form 20-F of CNOOC Limited; 2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made,] [CERTIFICATIONS 1. the Report fully complies with the requirements of Section 13(a) or 15(d) of the Exchange Act; and 2. the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of CNOOC Limited. Fanrong Li Chief Executive Officer and President Hua Zhong Chief Financial Officer] [CNOOC LIMITED Estimated Future Reserves and Income CNOOC’s 20% Ownership of Pan American Energy LLC SEC Parameters As of December 31, 2013 Guale Ramirez, P.E. Eric T. Nelson, P.C. TBPE License No. 48318 TBPE License No. 102286 Managing Senior Vice President - International Senior Vice President RYDER SCOTT COMPANY, L.P. [SEAL] TBPE Firm Registration No. F-1580 [SEAL]] [INDEPENDENT LETTER THE MISSAN OIL FIELDS IN EASTERN IRAQ ESTIMATED PROVED RESERVES AND FINANCIAL DATA, BASED ON SEC RULES Prepared for CNOOC LIMITED As at 31 st December, 2013 March, 2014 GAFFNEY, CLINE & ASSOCIATES (CONSULTANTS) PTE LTD This summary letter is based on Gaffney, Cline & Associates’ official report and has been provided at the request of CNOOC Limited.] [Hydrocarbon Liquids & Natural Gas Reserves Report at Year End 2013. Cerro Dragon, Anticlinal Funes, Piedra Clavada, Koluel Kaike and Acambuco in Argentina and Caipipendi in Bolivia CNOOC Limited Date Submitted: Project Number 411 N Sam Houston Parkway E, Suite 400, Houston TX 77060 rpsgroup.com Hydrocarbon Liquids & Natural Gas Reserves Report at Year End 2013 Cerro Dragon, Anticlinal Funes,] [TBPE REGISTERED ENGINEERING FIRM F-1580 FAX (713) 651-0849 1100 LOUISIANA STREET SUITE 4600 HOUSTON, TEXAS 77002-5294 TELEPHONE (713) 651-9191 February 26, 2014 CNOOC Limited No. 25, ChaoYangMenBei Dajie DongCheng District Beijing 100010 China Gentlemen: The properties subjected to the procedural audit by Ryder Scott account for a portion of CNOOC’s total net proved the procedural audit conducted by Ryder Scott] [February 27, 2014 CNOOC Limited c/o Nexen Energy ULC th 801-7 Calgary, AB T2P 3P7 Re: Gentlemen: . th Reserves included herein are expressed as reserves as represented by CNOOC. Gross reserves are defined as the total estimated petroleum to be produced from these properties after December 31, 2013. Working interest reserves are defined as that portion of the gross] [DeGolyer and MacNaughton 5001 Spring Valley Road Suite 800 East Dallas, Texas 75244 February 27, 2014 CNOOC Limited c/o Nexen Energy ULC 801-7 th Avenue S.W Calgary, AB T2P 3P7 Gentlemen: Reserves included herein are expressed as reserves as represented by CNOOC. Gross reserves are defined as the total estimated petroleum to be produced from these properties after December 31,] [April 17, 2014 100 F Street, N.E. Dear Sirs/Madams, Yours faithfully, Hong Kong] [CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM Hong Kong April 17, 2014] [CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM We consent to the incorporation by reference in Registration Statements on Form F-3 (File No(s). 333-187114 and 333-188261) of our reports dated March 28, 2014 relating to the consolidated financial statements of CNOOC Limited as of and for the year ended December 31, 2013, and the effectiveness of CNOOC Limited's internal control over] [[LETTERHEAD OF RYDER SCOTT COMPANY, L.P.] Consent of Independent Consultant [Corporate Seal] Ryder Scott Company, L.P. TBPE Firm Registration No. F-1580 Houston, Texas February 28, 2014] [[LETTERHEAD OF GAFFNEY, CLINE & ASSOCIATES (CONSULTANTS)PTE LTD.] YDH/dh/PS-13-2127&PS-13-2128/2014/L0090a th 27 CNOOC Limited No. 25, Chaoyangmenbei Dajie Dongcheng District Beijing 100010, P.R. China Dear Sir, Consent of Independent Consultant Yours sincerely, Gaffney, Cline & Associates (Consultants) Pte Ltd. Stephen A. Sakowski Technical Director] [Consent of Independent Consultant RPS Debbie Perkins Vice President [Place] Houston, Texas [Date] March 5, 2014] [[Letterhead of McDaniel & Associates Consultants Ltd.] Consent of Independent Consultant MCDANIEL & ASSOCIATES CONSULTANTS LTD. P. A. Welch, P. Eng. President & Managing Director McDaniel & Associates Consultants Ltd. 2200, Bow Valley Square 3, 255 - 5 Avenue S.W. Calgary, Alberta, T2P 3G6 Canada April 10, 2014] [DeGolyer and MacNaughton [Letterhead of Consent of Independent Consultant DeGolyer and MacNaughton Texas Registered Engineering Firm F-716 Dallas, Texas April 10, 2014]