Nigeria, Africa's biggest producer, accounts for a daily output of 2.6 barrels at peak production, but violence in the oil-producing south has reduced the figure by a quarter since January 2006.

More than 200 foreigners, mostly in the oil industry, have been kidnapped and later released by militants seeking a larger share of the region's oil wealth for the local people.

"The most dangerous areas have been abandoned by oil company operators," said Francis Perrin of the publication Arab Oil and Gas.

Despite the election of a new president, Umaru Yar'Adua, in April, "we don't have the impression the government has the means to find a lasting solution," Perrin said.

The International Energy Agency estimates that without the unrest, Nigerian daily outout would come to more than 3.0 million barrels.

But the agency has also noted that Nigeria's less vulnerable offshore production is gaining momentum, currently amounting to 900,000 barrels a day but with the capacity to eventually add 500,000 barrels.

The government's overall output target is 4.0 million barrels a day in 2010.