Exhibit 99.1

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)

DATE OF BOARD MEETING

The board of directors of CNOOC Limited (the "Company") (the "Board") announces that a meeting of the Board will be held on Thursday, 29 August 2019, whereat the Board will, amongst other matters, approve the interim results of the Company and its subsidiaries for the six months ended 30 June 2019 and may consider the payment of an interim dividend, if any.

By Order of the Board

CNOOC Limited

Wu Xiaonan

Joint Company Secretary

Hong Kong, 19 August 2019

As at the date of this announcement, the Board comprises:

Executive Directors Yuan Guangyu Xu Keqiang    
Non-executive Directors
Yang Hua (Chairman) Wang Dongjin (Vice Chairman) Independent Non-executive Directors
Chiu Sung Hong
Lawrence J. Lau
Tse Hau Yin, Aloysius Qiu Zhi Zhong