EXHIBIT 15.7

April 17, 2014

Securities and Exchange Commission

100 F Street, N.E.

Washington, D.C. 20549

United States

Dear Sirs/Madams,

We have read Item 16F of Form 20-F dated April 17, 2014 of CNOOC Limited and are in agreement with the statements contained in the second, third, fourth and fifth paragraphs under Item 16F on page 114 therein. We have no basis to agree or disagree with other statements of the registrant contained therein.

Yours faithfully,

/s/ Ernst & Young        

Hong Kong