[StormEye]

"Islamic State militants have set fire to Iraq’s largest oil refinery, escalating tensions in the region and raising questions about how much control ISIS could potentially gain over the world’s oil supply."

Refineries produce gasoline and various other compounds and fuels from crude oil. Destroying a refinery is not going to effect the world's oil supply. But I'm sure it will effect that region's supply of fuel for cars trucks etc.. Now if ISIS started destroying oil wells ...

[equaviator]

Let them destroy the wells. They can’t destroy the fields.