CNOOC Ltd. announced it completed the $15.1 billion acquisition of Nexen, a deal proposed in July.
CNOOC Chief Executive Officer Li Fanrong said the Canadian company has a large reserve base with high exploration prospects.
"We will thoroughly utilize the platform it provides to further our overseas business," he said in a statement.
The Canadian government approved the deal in December. In early February, the deal passed through the U.S. Committee on Foreign Investment. The deal needed U.S. approval because Nexen has assets in the Gulf of Mexico.
CNOOC said Calgary would serve as its headquarters for North and Central American operations. The Chinese company said it would seek to keep Nexen's employees, retaining Kevin Reinhart as the company's chief executive officer. Reinhart would continue to lead the company from Calgary.
Nexen announced Li would serve as the chairman of the company in a new board of directors comprised of Reinhart and other members of both entities.