Islamist rebels and extremist groups have seized control of most of Syria’s oil and gas resources, a rare generator of cash in the country’s war-battered economy, and are now using the proceeds to underwrite their fights against one another as well as President Bashar al-Assad, American officials say.
"...American officials say." It'd be nice to see actual people quoted.
Nevertheless, eminently plausible that some anti-Assad irregulars are trying to exploit what's now in their territory, though there are always logistical (and social) problems they need to solve.