ExxonMobil workers say the force majeure — or freedom from contractual obligations because of extraordinary circumstances — declared by the U.S.-based oil multinational on Nigeria's largest crude stream could last a month.

They say that's because of extensive damage to its 300,000 barrel-a-day Qua Iboe export terminal.

ExxonMobil has denied that militants bombed the facility. But a company security official said Friday the damage is too great for a system failure. Three workers spoke on condition of anonymity for fear of losing their jobs.

Futures sales of Nigerian oil have been affected by frequent declarations of force majeure. Qua Iboe terminal just restarted production after a month-long force majeure in June following an attack.

The militants want a bigger share of oil wealth for residents of the southern oil-producing region,