The company said its Nigerian affiliate, Star Deep Water Petroleum Limited, started crude oil production from the Agbami field on July 29.

The field is located 70 miles (112 kilometres) offshore from the centre of the oil-rich Niger Delta.

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"Initial production following from testing of a single well and dewatering flow-lines will increase, as planned, to reach a plateau of 250,000 barrels of crude oil and natural gas liquids per day by the end of 2009," it said.

It said the Agbami field, discovered in 1998, was the largest deepwater discovery in Nigeria with an estimated potential of 900 million barrels.

Chevron is the operator and has a 68.2 percent stake in the venture.

"Production from Agbami will now bring new energy supplies to the world market and help provide long term, sustainable returns to our shareholders," Ali Moshiri, president of Chevron Africa and Latin America, said.

In Nigeria Chevron operates and holds a 40 percent stake in 13 concessions covering 2.2 million acres (8,900 square kilometres), predominantly in the onshore and near-offshore regions of the restive Niger Delta.

In 2007, the company's total production from 32 fields averaged 353,000 barrels per day of crude, 14 million cubic feet of natural gas and 4,000 barrels of liquified petroleum gas (LPG), according to its website.

According to International Energy Agency statistics, Nigeria produced an average 2.13 million bpd in 2007, making it the 13th biggest producer in the world.

But it has slipped from its position as Africa's largest producer, being overtaken in April by Angola.

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