The regime of Syrian dictator Bashar Assad is stepping up its oil and gas purchases from the Islamic State, which is currently occupying a number of Syrian cities. Assad’s military is nominally engaged in a war to eradicate the Islamic State.

In fact, as The Wall Street Journal points out that oil trade with Syria’s Bashar Assad is currently the “Islamic State’s largest source of funds, replacing revenue the group once collected from tolls on the transit of goods and taxes on wages within its territory.” The oil trade is said to be putting a million dollars a day into the Islamic State’s coffers.

Conversely, Syria is now so dependent on ISIS fuel that the lights would start going out across Damascus if the supply line was interrupted. The WSJ notes that much of the gas comes from the area around the historic city of Palmyra, a UNESCO World Heritage site, which ISIS occupiers are currently demolishing.

The story gets even stranger because Assad has fallen behind in his payments, prompting ISIS to blow up a Syrian gas plant to send him a message.