US authorities give CNOOC permission to purchase Nexen

The deal, which had been backed by Canadian authorities yet still required US approval, is worth $15.1 billion and represents China’s largest ever foreign takeover.

Joshua Zive of Bracewell & Guiliani, a Washington-based lobbying firm said the approval for CNOOC's latest deal "is likely to be viewed as a positive development. That, in the current climate, is a moment of significance.”

Nexen's shares rose two percent after it announced the approval by the US regulators. The firm said it now expects to complete the deal in the week beginning 25 February.