HONG KONG (AP) — Chinese oil company CNOOC says it has completed its $15.1 billion purchase of Canadian energy producer Nexen.

State-owned CNOOC said in a statement that the acquisition was completed on Monday.

China's biggest overseas energy deal was finalized after winning approval from a U.S. agency that reviews takeovers by foreign companies for national security implications. The agency had a say because Nexen has Gulf of Mexico oil and gas fields.

Canada approved the deal despite worries it could lead to a flood of takeovers in the country's oil sands sector. Canada's prime minister said approval of similar deals in the future would be unlikely.

Calgary-based Nexen also operates in western Canada, the North Sea, Africa and the Middle East.