In December, PetroChina agreed to invest $2.2 billion for a 49.9 percent stake in a Canadian shale gas field being developed by Encana Corp.

Last month, another Chinese state-owned oil producer, CNOOC Ltd., completed a $15.1 billion acquisition of Canadian energy producer Nexen. It was Canada's biggest overseas energy deal to date.

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

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