ISIS, the terrorist group that has taken over a large swath of eastern Syria and northern Iraq, is making millions of dollars selling black-market crude from seized oil wells, Iraqi officials say.

Though the black-market price is far below the going rate of just over $100 a barrel, ISIS could be raking in up to $3 million a day, Foreign Policy reports. Some reports says ISIS is getting only $25 a barrel from Turkish traders.

Still, that is enough to boost ISIS in the short term. It also has raided banks and seized U.S.-supplied weapons when Iraqi soldiers laid down their arms and fled during the ISIS invasion.

ISIS seized four small oil fields during its takeover of Iraqi areas earlier this year. Two are near the northern city of Mosul and two are farther south, near Tikrit, NBC News reports.

About 80 wells compose the four fields and are now capped, NBC reports, making them unable to pump new oil. Additionally, Foreign Policy reports, the wells will not be able to continue to function because ISIS doesn't have people skilled in keeping them maintained.

The Iraqi government and Kurdish leaders control larger oil fields in the country, but Iraq says ISIS still has been able to move its oil to Syrian refineries to make low-quality gas oil and gasoline. It is then returned to Mosul to be sold at gas stations.

Large amounts of the oil are sold to Turkish traders through smugglers, NBC reported.

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