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Aerial images show illegal oil refineries in Nigeria's delta region

Akintunde Akinleye / Reuters

A view of an illegal oil refinery is seen in Ogoniland outside Port Harcourt in Nigeria's Delta region March 24, 2011.Crude oil thieves -- known locally as "bunkerers" -- have been a fact of life for years in Africa's biggest oil and gas industry, puncturing pipelines and costing Nigeria and foreign oil firms millions of dollars in lost revenues each year.

Akintunde Akinleye / Reuters

Smoke rises from an illegal oil refinery in Ogoniland outside Port Harcourt in Nigeria's Delta region.

Akintunde Akinleye / Reuters

Oil surfaces on water near an illegal oil refinery in Ogoniland outside Port Harcourt in Nigeria's Delta region March 24, 2011.

 Here's an article that provides some context for the existence of "bush refineries."