China Oilfield Services, a listed subsidiary of China’s third-largest oil and gas producer, is to buy Norwegian rival Awilco ­Offshore for about $2.5bn in a deal that would give it access to drilling technology and expand its international operations.

COSL, China’s largest offshore oil services group, said it would pay NKr85 a share in cash for the Norwegian company, a 19 per cent premium to the closing price on Friday.