BEIJING - China's largest offshore oil company, CNOOC Ltd, agreed to pay $1.08 billion to buy a stake in a shale oil and gas project in the United States, in line with moves to increase the use of gas in China's energy mix.

CNOOC will buy a 33.3 percent interest in US company Chesapeake Energy Corp's Eagle Ford shale project in southern Texas. The transaction is expected to be completed in the fourth quarter of this year, said a company statement.

Chesapeake anticipates the project will reach its peak production of 400,000 to 500,000 barrels of oil equivalent a day in the next decade, said the statement.