CNOOC, China's largest offshore oil and gas producer, said in a statement on its website that the company paid about 15.1 billion U.S. dollars for Nexen's common and preferred shares.

　　Wang Yilin, chairman of CNOOC, said the company is delighted to have acquired a leading international platform through the acquisition of Nexen.

　　"We strongly believe that this acquisition is a good strategic fit for us and will create long-term value for our shareholders," Wang said.

　　The statement said Kevin Reinhart will continue to serve as CEO of Nexen, which will operate as a wholly-owned subsidiary of CNOOC.

　　Li Fanrong, CEO of CNOOC Limited, a listed subsidiary of the company, will chair the new Nexen board, the statement said.

　　Li said Nexen owns a large resource and reserve base and high-potential exploration prospects. "We will thoroughly utilize the platform it provides to further our overseas business."

　　The deal was first announced in July 2012. It is the largest overseas acquisition ever made by a Chinese company.

　　CNOOC Limited shares opened 0.78 percent lower at 15.2 HK dollars (about 1.96 U.S. dollars) in Hong Kong on Tuesday.