[FORM 20-F (Mark One) ¨ OR ý For the fiscal year ended December 31, 2011 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] [Subsidiaries As of December 31, 2011, 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 24 August 2011 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 Estimated Future Reserves and Income Attributable to Certain Leasehold Interests And Derived Through Certain Production Sharing Contracts SEC Parameters As of December 31, 2011 Herman G. Acuna, P.E. Texas P.E. License No. 92254 Managing Senior Vice President – International RYDER SCOTT COMPANY, L.P. TBPE Firm Registration No. F-1580 RYDER SCOTT COMPANY PETROLEUM CONSULTANTS] [EXECUTIVE REPORT FOR RESERVES ASSESSMENT OF THE MISSAN OIL FIELDS IN EASTERN IRAQ ST AS OF 31 Prepared for CHINA NATIONAL OFFSHORE OIL CORPORATION LIMITED MARCH, 2012 CONFIDENTIAL This document contains proprietary and confidential information which may not, without the express written permission of Gaffney, Cline & Associates, be released to any third party in any form, copied in any] [January 24, 2012 CNOOC Limited No. 25, Chaoyangmenbei Dajie Dongcheng District Beijing, 100010 China Re: Estimated Proved Reserves and Future Net Revenue Interests Owned by OOGC America, Inc. Constant Prices and Expenses Gentlemen: ESTIMATED REMAINING NET RESERVES FUTURE NET REVENUE Present Worth RESERVE] [February 9, 2012 CNOOC Limited th 1600, 555 – 4 Calgary, Alberta T2P 3E7 Attention: Reserves Review Committee of the Board of Directors of CNOOC Limited. Re: Ladies and Gentlemen: th The following table sets forth the proved reserve estimates using constant prices and costs. T a ble 1 : Company Net Proved Reserves Synthetic Natural Oil Location of Reser] [PAN AMERICAN ENERGY CHILE Estimated Future Reserves and Income Attributable to the 100 Percent Working Interest in the Coiron Block, Chile SEC Parameters As of December 31, 2011 í Guale Ram í Guale Ram TBPE License No. 48318 Managing Senior Vice President RYDER SCOTT COMPANY, L.P. TBPE Firm Registration N o . F-1580 RYDER SCOTT COMPANY PETROLEUM CONSULTANTS PAN AMERICAN] [& Hydrocarbon Liquids Reserves Audit Report 2011 Ó Cerro Drag Koluel Kaike and Acambuco Areas, Argentina Prepared For: Pan American Energy, LLC January 2012 Luis V. Bacigalupo, P.Eng. Senior Vice President. Alberta P.Eng. Permit 23579 411 North Sam Houston Parkway E., Suite 400 , Houston, Texas 77060-3545 T E r psenergy@rpsgrou p . com W ww w . rpsgrou p]