PetroChina is to buy a 49.9% stake in a natural gas project in Alberta from Encana of Canada.
According to Encana, the project contains supplies equivalent to nearly nine billion barrels of oil. PetroChina will pay $US2.2 billion for the stake.
Earlier this week, PetroChina said it would buy BHP Billiton's stake in a liquefied natural gas project in Australia.
The BBC reports that CNOOC, another Chinese firm, received approval from the Canadian government on 7 December to take over the oil firm Nexen in a deal worth $US15.1 billion.
In a separate announcement, the Canadian government also cleared the takeover of gas producer Progress Energy Resources by Petronas of Malaysia for $US5.5 billion.
