According to some media reports, ISIS runs a self-sustaining economy across territory it controls in Syria and Iraq, pirating oil while exacting tribute from a population of at least eight million.
More than 40 per cent of ISIS oil revenue has been affected by US-led strikes over the past month, the top US military officer said in testimony to a congressional committee on Tuesday.
"We estimate that approximately 43 per cent of the revenue stream that ISIL derives from oil has been affected over the past 30 days," said US General Joe Dunford, chairman of the Joint Chiefs of Staff, using an acronym for the militant group.
© Thomson Reuters 2015