The Islamic State terrorist group has been reaping huge profits from oil smuggling. Contraband oil is shipped from ISIL bastions. Illegal oil exports quickly became the main driver of ISIS revenues. "ISIL is one of the wealthiest militant groups," Adam Szubin, acting under secretary for Terrorism and Financial Intelligence with the Treasury, told an audience at Chatham House in London. The US official estimated that the ISIL militants could have plundered over $1.5 billion in total. ISIL has made more than $500 million trading oil in significant volumes on the black market. Szubin said militants had looted up to $1 billion from bank vaults in Syria and Iraq. Besides, the extremist group robbed the local population at the seized areas. So the US-led military coalition is taking joint efforts to cut oil smuggling routes and keep track of oil refineries, tankers, and stocks on the Islamic State-held territory.