The US claims that a combination of factors have reduced ISIS's oil revenues by half, Reuters reports.
Due to the declining price of oil, air strikes and anti-smuggling measures, the terror group is now only making about $250 million per year by selling oil.
"The number that we had been giving previously until about early this year was $500 million a year off of oil sales. I think they're substantially less than that now," said a Treasury Department official. "I think they probably make about half of what they previously made."