[FORM F-3 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 CNOOC Limited Issuer Hong Kong (State or Other Jurisdiction of Incorporation or Organization) Not Applicable (I.R.S. Employer Identification Number) 65th Floor, Bank of China Tower One Garden Road, Central Hong Kong Tel +852 2213 2500 National Corporate Research, Ltd. 10 East 40th Street, 10th Floor New York, NY 10016 (800)] [Dated as of July 30, 2009 NEXEN INC. and DEUTSCHE BANK TRUST COMPANY AMERICAS SECOND SUPPLEMENTAL INDENTURE to the TRUST INDENTURE Dated as of May 4, 2007 Second Supplemental Indenture NEXEN INC. Issuer DEUTSCHE BANK TRUST COMPANY AMERICAS Trustee THIS SECOND SUPPLEMENTAL INDENTURE (this “ RECITALS OF THE COMPANY WHEREAS Original Indenture WHEREAS WHEREAS WHEREAS WHEREAS 2019 Notes 2039 Notes] [NEXEN INC. and DEUTSCHE BANK TRUST COMPANY AMERICAS THIRD SUPPLEMENTAL INDENTURE to the TRUST INDENTURE Dated as of May 4, 2007 Third Supplemental Indenture CBCA Nexen AmalCo DEUTSCHE BANK TRUST COMPANY AMERICAS Trustee THIRD SUPPLEMENTAL INDENTURE (this “ RECITALS OF THE COMPANY WHEREAS Nexen NPII Amalgamation WHEREAS WHEREAS Original Indenture First Supplemental Indenture Second Supplemental Indenture Indenture Securities WHEREAS WHEREAS] [The proposed text of the Fourth Supplemental Indenture is set forth below. The text of the Fourth Supplemental Indenture as executed and delivered may include minor changes from the proposed text, as deemed appropriate by the parties thereto. Dated as of March [ ], 2013 NEXEN INC. and DEUTSCHE BANK TRUST COMPANY AMERICAS and CNOOC LIMITED FOURTH SUPPLEMENTAL INDENTURE to] [THIS SECOND SUPPLEMENTAL INDENTURE (the “Supplemental Indenture”) dated as of February 4, 1999. BETWEEN: CANADIAN OCCIDENTAL PETROLEUM LTD. OF THE FIRST PART OF and - CIBC MELLON TRUST COMPANY OF THE SECOND PART WITNESSETH THAT: WHEREAS AND WHEREAS AND WHEREAS AND WHEREAS NOW THEREFORE 1. INTERPRETATIONS AND AMENDMENTS 1.1 Supplemental Indenture This “Supplemental Indenture”, “hereto”, “herein”, “hereof’, “hereby”, “hereunder” and] [Dated as of February 24, 2013 . NEXEN INC -and- CIBC MELLON TRUST COMPANY SIXTH SUPPLEMENTAL INDENTURE to the TRUST INDENTURE Dated as of April 28, 1998 TABLE OF CONTENTS 1. INTERPRETATIONS AND AMENDEMENTS 2 1.1 Supplemental Indenture 2 1.2 Definitions in Indenture 3 1.3 Interpretation not Affected by Headings 3 1.4 Number; Persons 3] [Dated as of March ●, 2013 NEXEN INC. -and- CIBC MELLON TRUST COMPANY -and- THE BANK OF NEW YORK MELLON -and- CNOOC LIMITED SEVENTH SUPPLEMENTAL INDENTURE to the TRUST INDENTURE Dated as of April 28, 1998 TABLE OF CONTENTS 1. INTERPRETATIONS AND AMENDEMENTS 2 1.1 Supplemental Indenture 2 1.2 Definitions in Indenture 2 1.3 Interpretation not Affected by Headings 3] [OPINION OF DAVIS POLK & WARDWELL LLP March 7, 2013 CNOOC Limited 65th Floor, Bank of China Tower One Garden Road, Central Hong Kong Ladies and Gentlemen: We, as your counsel, have examined originals or copies of such documents, corporate records, certificates of public officials and other instruments as we have deemed necessary or advisable for the purpose of rendering] [March 5, 2013 The Directors CNOOC Limited 65th Floor, Bank of China Tower One Garden Road, Central Hong Kong Dear Sirs, We are aware of the incorporation by reference in this Registration Statement on Form F-3 of CNOOC Limited for the registration of debt securities and guarantees of CNOOC Limited of our report dated August 21, 2012 relating to the] [Consent of Independent Registered Public Accounting Firm Certified Public Accountants Hong Kong March 5, 2013 EX-23.1 18 dp36639_ex2301.htm EXHIBI 23.1] [] [1.]