An article has appeared in the New York Post, presumably to convince us all how dangerous ISIL is. They have lots of money, see?
This article uses a lot of guesswork. It says ISIL is smuggling oil by paying off border guards. Smuggling oil is awfully hard by truck and oil trucks make easy targets in the middle of the desert.
The article says ISIL controls "up to 11" oilfields. In other words, the "intelligence sources" have no idea how much oil ISIL has or whether ISIL are successful pumping it and selling it. Maybe ISIL, primarily an army of thugs, can pump oil. Maybe they can't. In any event, the oil fields can be shut down quickly with a couple of drone strikes.
The article says ISIL is getting money through extortion and other criminal enterprises. That is entirely believable. But money is hard to hide and ISIL won't have an easy time buying weapons with it
The US goes ahead with its idiotic plan to arm anti-Syrian rebels, who are known to be allies of ISIL. Then the anti-Syrian rebels, our supposed allies, will be able to sell weapons to ISIL, and the US will find itself giving weapons to the group it claims to be fighting.