Waste Oil Dumps Threaten Towns in Northern Iraq As much as 40 percent of the petroleum processed at Iraq's damaged and outdated refineries pours forth as black oil, the heavy, viscous substance that used to be extensively exported to more efficient foreign operations for further refining. But the insurgency has stalled government-controlled exports by taking control of roadways and repeatedly hitting pipelines in the area, Iraqi and American officials have said.

So the backed-up black oil — known to the rest of the world as the lower grades of fuel oil — was sent along a short pipeline from Baiji and dumped in a mountainous area called Makhul.