(Hong Kong, July 20, 2011) - CNOOC Limited (the "Company", NYSE: CEO, SEHK: 0883) announced today that CNOOC Luxembourg S.¨¤ r.l, an indirect wholly-owned subsidiary of the Company has entered into an Arrangement Agreement to acquire OPTI Canada Inc ("OPTI"). The aggregate value of the consideration of the transaction is approximately US$2.1 billion, which includes aggregate cash consideration of US$1.25 billion payable to the holders of the OPTI shares (US$34 million) and the Second Lien Noteholders (US$1.216 billion). In addition, due to a change in control of OPTI as a result of the transaction, OPTI will be required to offer to repay the holders of its outstanding First Lien Notes (US$825 million in principal amount) pursuant to the indentures governing the First Lien Notes. The transaction will be effected by way of a plan of arrangement through concurrent proceedings under the Companies’ Creditors Arrangement Act (Canada) and the Canada Business Corporations Act.

The proposed transaction must be approved by the Second Lien Noteholders at a special meeting that is expected to be held in September,2011. Noteholders representing approximately 55.2% of the principal amount of the Second Lien Notes have executed support agreements pursuant to which, among other things, they have agreed to vote in favour of the transaction.

The proposed transaction is also subject to certain terms and conditions, including, among other things, applicable government and regulatory approvals by the relevant authorities in Canada and the People’s Republic of China, and Canadian court approval. The transaction is expected to be completed in the fourth quarter of 2011. Upon completion of the transaction, OPTI will become an indirect wholly-owned subsidiary of the Company, and all of the Second Lien Notes will be transferred or assigned, directly or indirectly, to a subsidiary of the Company. All existing options, warrants and other rights to purchase OPTI shares will be cancelled.

The principal asset of OPTI consists of a 35% working interest in the Long Lake and three other project areas located in the Athabasca region of northeastern Alberta. Long Lake project includes steam assisted gravity drainage ("SAGD") Operation and an Upgrader. Nexen Inc. ("Nexen"), a Canadian-based global energy company, holds the remaining 65% and is the sole operator. The Long Lake SAGD Operation is expected to have through-put rates of approximately 72,000 barrels per day of bitumen at full production. It is anticipated that the Long Lake Upgrader will ultimately produce approximately 58,500 barrels per day of products, primarily Premium Sweet Crude (PSCTM).

As disclosed in OPTI’s disclosure documents filed with securities regulatory authorities in Canada, OPTI’s working interest share, before royalties, of raw bitumen reserves and resources on its oil sands leases is estimated to be 195 million barrels of proved reserves, 534 million barrels of probable reserves, 1,100 million barrels of contingent resources and 335 million barrels of prospective resources. These reserves and resources are estimated to be sufficient to support approximately 430,000 barrels per day (150,000 barrels per day net to OPTI) of bitumen production.

Mr. Yang Hua, Chief Executive Officer of the Company stated, "We are pleased to expand our presence in the oil sands business after our successful investment in MEG. We believe that the upside potential of the acquired assets will benefit the shareholders of CNOOC Limited."

Mr. Li Fanrong, President of the Company said, "We look forward to working with our new partner Nexen, to optimize value from the Long Lake Project and the three other jointly owned oil sands leases."

The Company’s financial advisors are BMO Capital Markets and CIBC World Markets. The Company’s legal advisor is Gowling Lafleur Henderson LLP.