China National Offshore Oil Company Limited (CNOOC Ltd.) announced Wednesday that its four oil and gas fields in east China's Bohai Sea area had started production.

The four oil and gas fields are JinZhou 25-1 South (JZ25-1S), Caofeidian (CFD)18-2, BoZhong (BZ) 13-1 and BoZhong 34-1 North (BZ34-1N).

Among them, the JZ25-1S oil and gas field began production in mid-December. It is expected to produce more than 20,000 barrels of oil and 53 million cubic feet of natural gas daily by 2012.