CNOOC : ANNOUNCEMENT

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 Code: 00883)

AND

CNOOC Finance (2003) Limited

(incorporated in the British Virgin Islands with limited liability)

US$300,000,000 5.500% Guaranteed Noted due 2033

(Stock code: 02568)

unconditionally and irrevocably guaranteed by

(Incorporated in Hong Kong with limited liability under the Companies Ordinance)

(Stock code: 00883)

ANNOUNCEMENT

This is an announcement jointly issued by CNOOC Limited (the "Company") pursuant toRules 13.10B, 37.44 and 37.48(b) of the Rules Governing the Listing of Securities on TheStock Exchange of Hong Kong Limited (the "Listing Rules") and CNOOC Finance (2003)Limited, a wholly-owned subsidiary of the Company ("the "Issuer"), pursuant to Rules 37.44and 37.48(b) of the Listing Rules in relation to the US$300,000,000 5.500% notes due 2033(stock code: 02568) issued by the Issuer and guaranteed by the Company (the "Notes") listed on The Stock Exchange of Hong Kong Limited (the "Hong Kong Stock Exchange") and theLuxembourg Stock Exchange.

Please refer to the following notice which has been published by the Issuer on the website of the Luxembourg Stock Exchange on 26 July 2018 in respect of the request for delisting of the Notes from the official list of the Luxembourg Stock Exchange and from trading on the regulated market of the Luxembourg Stock Exchange.

The Notes (stock code: 02568) will continue to be listed on the Hong Kong Stock Exchange.

By Order of the Board

CNOOC Limited

Li Jiewen

Joint Company Secretary

Hong Kong, 26 July 2018

As at the date of this announcement, the sole director of CNOOC Finance (2003) Limited is CNOOC Limited.

As at the date of this announcement, the directors of CNOOC Limited comprises:

CNOOC Finance (2003) Limited

(the "Issuer")

US$300,000,000 5.500% Guaranteed Notes due 2033 unconditionally and irrevocably guaranteed by CNOOC Limited (ISIN USG21886AB53)

(the "Notes")

Delisting request filed with the Luxembourg Stock Exchange

On July 26, 2018, the Board of Directors of the Issuer took the decision to request the de-listing of its Notes from the official list of the Luxembourg Stock Exchange and from trading on the regulated market of the Luxembourg Stock Exchange. A delisting submission, requesting the effective delisting date to be as soon as possible, has been filed with the Luxembourg Stock Exchange on July 26, 2018.

The Notes are currently also, and will continue to be, listed on the Hong Kong Stock Exchange.

The Issuer will make another publication upon the Luxembourg Stock Exchange granting the delisting request and notifying it of the effective date of the delisting of the Notes.

If you need any further information, please do not hesitate to contact Wu Tao by phone 8610-8452-1730 or by mail atwutao2@cnooc.com.cn.

British Virgin Islands, July 26, 2018

For and on behalf of the Board of Directors-CNOOC Finance (2003) Limited