A recent WSJ article raises the question of how much ISIL is raising from sales of looted cultural property and how much it is getting from oil. This can be seen to have been related to the UNSC debate on resolution 2199.
In November the U.N. estimated Islamic State's revenue from oil ranged between $846,000 to $1.6 million a day. However, the Pentagon has assessed that oil was no longer the main source of revenue for Islamic State. Western diplomats have said this was due to air strikes on oil installations and a plunge in oil prices that has affected black market prices as well. The U.N. report said Islamic State was raising about $96,000 to $123,000 per day from ransom payments. The resolution calls upon "all Member States to prevent terrorists from benefiting directly or indirectly from ransom payments or from political concessions and to secure the safe release of hostages."Michelle Nichols, 'U.N. Security Council ups pressure on Islamic State financing', Reuters Thu Feb 12, 2015.