CNOOC Ltd, the country's largest offshore oil producer, said Friday its revenues from oil and gas sales rose 13.3 percent year-on-year due to increased output in the first quarter of 2013.

The revenues, which have yet to be audited, reached 55.31 billion yuan ($8.89 billion) in the first quarter, the company said in a statement. The growth was much faster than the annual rise of 2.9 percent in 2012.

Net output of oil and gas jumped 17.3 percent year on year to 93.6 million barrels in the first quarter, compared with the annual 3.2-percent gain in 2012.

The company, listed in New York and Hong Kong, attributed the higher output to its acquisition of Canadian energy firm Nexen Inc and production from new oil fields and overseas projects.

CNOOC completed the deal to acquire Nexen in February, paying about $15.1 billion for all of the firm's common and preferred shares in the biggest ever overseas takeover made by a Chinese company.

Nexen runs oil sands and shale gas projects in western Canada. It also conducts conventional exploration and development operations, primarily in the British North Sea, off the shores of West Africa and in the Gulf of Mexico.

In the first quarter, CNOOC discovered four new oil fields in Chinese waters, according to the statement.