The falling world price of crude oil, rising costs and restrictions on overseas operations affected profits in the E&P unit, the company said. Still, this division remained the company's most profitable.

The exploration of natural gas in the Sichuan Basin achieved a major breakthrough, with new proven reserves in the Longwangmiao gas reservoir of the Anyue gas field standing at 187.5 billion cubic meters.

Due to sluggish demand for refined products and government price controls, the refining and chemicals business lost 24.3 billion yuan last year, narrowed from 43.5 billion yuan in 2012.

China's major oil refiners have been told to coordinate production and distribution and avoid raising gasoline and diesel prices. They've been ordered to ensure steady supplies even when global crude oil prices increase.

The company's natural gas and pipeline business swung from a loss of 2.1 billion yuan in 2012 to a profit of 28.9 billion yuan last year.

The improvement reflected a change in China's natural gas pricing mechanism.

In July, the National Development and Reform Commission, China's top planner, raised natural gas rates for industrial users by an average of 15 percent.

"As the nation accelerates a transition to natural gas to cut air pollution [from coal], we will see more profits for natural gas producers from higher prices," said Lin Boqiang, director of the China Center for Energy Economic Research at Xiamen University.

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