Energy experts say widespread thefts of crude oil in Nigeria cost the country $7 billion a year.
The International Energy Agency gave the estimate Tuesday in a monthly report on oil production around the world. The agency noted that Royal Dutch Shell PLC, the country's largest oil producer, had already said its quarterly results would be down about 20 percent after a series of pipeline theft attacks.
The agency also said that crude oil production in Nigeria dropped to its lowest level in two and a half years in October to about 1.95 million barrels a day because of flooding in the oil-rich Niger Delta.
Militant attacks in the region drop after a 2009 government-sponsored amnesty program. However, crude oil thefts have skyrocketed, likely supported by security forces and politicians.