Calgary-based Canadian energy company Athabasca Oil Sands Corp will sell its 40-percent share of the Dover oil sand project to China's largest oil and gas developer, PetroChina Co, for $1.2 billion.

The transaction will make the Chinese company the sole owner of the project, which is located in Alberta.

In 2010, PetroChina bought 60 percent of the project from Athabasca through its subsidiary Brion Energy Corp, and was awaiting approval from the Canadian government to purchase the remaining 40 percent.

In 2012, the Canadian government published a new regulation that forbade foreign State-owned companies from owning all of any Canadian large oil sand project, meaning PetroChina will be the last such foreign company to buy 100 percent of a Canadian oil sand project.

The sale of the project, which has a daily output of 250,000 barrels, recently got final approval from the Alberta government.