Who is buying ISIL's oil?

Turkey has been forced to deny Russian allegations that it buys oil from the armed group, and says Assad is a customer.

On the face of it, it looks like any state-run oil industry.

Engineers, managers and traders, all help extract, refine and distribute oil, which makes its way across Syria and Iraq as well as overseas.

But this is no state-run company. This is the Islamic State of Iraq and the Levant's (ISIL) lifeline - a business that provides the armed group with more revenue than any other source.

Oil helps to fund its war in Syria and Iraq, as well as to provide electricity to the 10 million people living under ISIL control.

But despite the oil trade being targeted by the US-led coalition against ISIL, the business continues to thrive.

And many people are increasingly asking why.