CNOOC Limited is the major Hong Kong listed subsidiary of China National Offshore Oil Corporation. CNOOC Ltd is listed in Hong Kong SEHK:_0883 and also trades in New York NYSE:_CEO. CNOOC Ltd's parent, CNOOC Group, is the third largest of the "Big Three" Chinese oil companies, and traditionally specialised in offshore upstream exploration and production, whereas CNPC Group specialised in onshore upstream exploration and production, and Sinopec Group specialised in refining and marketing. These distinctions are now increasingly blurred as the three companies compete in all areas. All of the "Big Three" have vested the majority of revenue producing assets in listed Hong Kong subsidiaries. CNPC into PetroChina, Sinopec Group into Sinopec Limited, and CNOOC Group into CNOOC Limited. China Oilfield Services (COSL) is another subsidiary of CNOOC Limited listed in Hong Kong.
Contributions by In ictu oculi, Svgalbertian, and Haeinous.