Changqing was after Daqing Oilfield, the annual output of which had already broken the 40-million-tonne mark this year, the subsidiary of China's largest oil and gas producer PetroChina said in a press release.

The whole-year output in 2011 is expected to hit 40.6 million tonnes of oil equivalent, the statement said, adding that natural gas accounted for about half of the output.

Changqing's output in 2010 was 35 million tonnes of oil equivalent, with 18.3 million tonnes of crude oil and 21.1 billion cubic meters of natural gas.

Changqing Oilfield has seen proven oil and gas reserves increase by an average of 200 million tonnes and 200 billion cubic meters, respectively, in each of the past four years.

Meanwhile, its output has grown by an average of 5 million tonnes for four consecutive years, representing the fastest growth nationwide.

Changqing Oilfield added that its output of oil equivalent is expected to rise to 50 million tonnes in 2013.