Money from illicit oil sales is no longer the main source of revenue for the Islamic State, Pentagon Press Secretary Rear Adm. John Kirby told reporters at the Pentagon Tuesday.

Oil smuggling had become a crucial source of revenue for the group, which holds a handful of oil fields in Iraq and Syria. Oil profits set the extremist organization apart from other terrorist groups that are more reliant on outside donations. But oil production is also a vulnerability for the group, as it provided the U.S.-led coalition with relatively easy targets to hit with airstrikes.

Over the summer, before U.S. airstrikes began, the Islamic State was believed to be producing more than 80,000 barrels a day. Because it was selling the oil on the black market, the group took a major discount compared to global market prices, but experts still estimated it was collecting between an estimated $1 million to $3 million a day. […]