Citing multiple sources, the Israeli business press are now reporting that Israel is the main recipient of ISIS oil: 

Kurdish and Turkish smugglers are transporting oil from ISIS controlled territory in Syria and Iraq and selling it to Israel, according to several reports in the Arab and Russian media. An estimated 20,000-40,000 barrels of oil are produced daily in ISIS controlled territory generating $1-1.5 million daily profit for the terrorist organization.

The oil is extracted from Dir A-Zur in Syria and two fields in Iraq and transported to the Kurdish city of Zakhu in a triangle of land near the borders of Syria, Iraq and Turkey. Israeli and Turkish mediators come to the city and when prices are agreed, the oil is smuggled to the Turkish city of Silop marked as originating from Kurdish regions of Iraq and sold for $15-18 per barrel (WTI and Brent Crude currently sell for $41 and $45 per barrel) to the Israeli mediator, a man in his 50s with dual Greek-Israeli citizenship known as Dr. Farid. He transports the oil via several Turkish ports and then onto other ports, with Israel among the main destinations.