Satellite images show that  the Islamic State group (IS) has dug hundreds of pits in Mosul oilfields to store and refine crude oil after its refineries and oil tankers were destroyed in ground and air assaults in terrorists-held regions, FarsNews reported.

According to The Washington Post, makeshift refineries popping up in oil fields controlled by the IS are evidence that the militants are finding workarounds after losing much of their oil infrastructure to airstrikes. These micro-refineries consist of pits for storing crude and a portable metal furnace used to refine raw petroleum into fuel.

 The tiny refineries are partly offsetting huge losses in income resulting from the disruption of traditional oil production in northern Iraqi fields controlled by the IS since mid-2014. However, these refineries are not the ideal facility to generate oil.  Omar Lamrani, Senior Analyst for Stratfor, a private, Texas-based intelligence company said:  “It’s not the ideal way to do it, so their revenue is going down. But it still works.”

In the end of May, Iraqi troops launched an offensive to retake the city of Fallujah from IS militants, announcing the liberation of a gas refinery in the southern part of the city. The Iraqi forces also recaptured from IS’s hands key parts of the northern refinery town of Beiji.