Isis has become the most potent terror organization, they have done that to a large extend by finding better sources of income than comparable organizations primarily through their exploitation of oil fields from territory they conquered. Since ISIS is internationally condemned they have troubles selling their oil, however reports show that although ISIS sells its oil for only 20$ per barrel they still earn more than 2 million dollars per day. Clearly then the most effective way to stop the threat posed by ISIS is to cut down their income gained from selling oil at the back market. Steps have already been taken to stop this black market activity Kurdish Peshmerga militants have arrested about 360 suspects on dealing oil. The US has also been working with the Kurdistan Regional Government to identify oil routes, trucks and traders in an effort to block smuggling. Recently ISIS has been struggling to conquer more territory trough the frequent airstrikes by the American government. German news has reported that according to reports from the German Intelligence Agency BND Oil production capacity has sharply shrunken six fold, it looks like the allies are making progress.

http://rt.com/news/203723-isis-iraq-oil-smuggle/