The Shell oil company said it is losing the equivalent of 30,000 barrels of crude oil per day in Nigeria, due to attacks against its installations.
The unrest in Nigeria, which is Africa's biggest oil producer, helped drive oil prices to a record high above $126 on Friday, analysts said.
According to Chidi Izuwah, a spokesman for the Shell Petroleum Production Company, the loss in production translates to $3.47 million in lost revenue every day.
Shell is Nigeria's largest oil operator and accounts for around half of the country's 2.1 million barrels per day in output.
A surge in attacks on its facilities has forced it to cut back on production.
Sabotage
Armed groups in the Niger Delta, most prominently known as the Movement for the Emancipation of the Niger Delta (MEND), have sabotaged several supply pipelines owned by Shell and other oil operators in the region.
MEND emerged in early 2006 as the leading group calling for a greater share of Nigeria's oil revenue.
Besides attacking facilities, it has seized local and expatriate oil workers as hostages.
Overall, violence in the Niger Delta has reduced Nigeria's total production by a quarter in the past two years.