A significantly oil exporter before the civil war, Syria has found itself extremely oil-poor, with almost all the oil producing regions of the country now under ISIS control. This has been a windfall for ISIS, which has allowed local communities to keep running the oil and has been raking in heavy tax dollars from it.
That’s made oil production in ISIS territory a major focus, with both the US and Russia pounding what is basically civilian infrastructure, on the theory that they are dramatically cutting ISIS’ income by virtue of lowering their exports. They’re not halting them though, and the income loss may be overstated.
ISIS doesn’t sell oil on the traditional international market, of course. They sell the oil and refined products, at a discount, to smugglers who take it elsewhere, including large amounts that ends up in other parts of Syria that aren’t under ISIS control. As that excess oil availability falls, so does the discount, and those parts of Syria are seeing a major price increase, parts of which are going right into ISIS’ pockets.
This is compounded by Syria not importing a lot of oil from overseas, except for enough to keep their military running, meaning private industry is going to these smugglers, and may ultimately be willing to pay above-market prices for ISIS oil, since the war is making supply so scarce.