CNOOC said it's paying US$2.27 billion (euro1.84 billion) for the deal that covers part of the oil-rich Niger Delta region. The company will also pay US$424 million (euro343.43 million) for financial, operating and capital expenses, the firm said in a statement.

"The completion of this transaction represents a milestone in our efforts to expand into the world's most prolific oil and gas basins," said Fu Chengyu, chairman and chief executive officer of CNOOC.

Chinese oil companies have been pursuing energy supplies to fuel the country's booming economy.

CNOOC has recently announced other agreements to explore for oil in Chinese waters and off the coast of Western Australia.

The initial agreement for Nigeria was announced last January, but the Nigerian and Chinese governments had not yet approved it.

Last year, CNOOC offered US$18.5 billion for Los Angeles-based Unocal, but withdrew its bid in August after opposition from U.S. politicians.

The China National Offshore Oil Corp. owns 70 percent of CNOOC's shares.

On Wednesday, News Agency reported that CNOOC plans to invest 100 billion yuan (US$12.5 billion; euro10.2 billion) in oil and gas exploration and production through 2010.

The report quoted Tan Dongling, a manager with CNOOC's development and planning department, as saying the spending would help raise CNOOC's production in 2010 to 50 million metric tons of oil equivalent, including 38 million metric tons of crude oil and 12.6 billion cubic meters of natural gas.