David Cohen, the Treasury Department's under secretary for terrorism and financial intelligence, said Daesh earns about $1 million each day in oil sales.
"The group has netted approximately $20 million in ransom payments this year. It also raised funds through local extortion and crime, like robbing banks," said the US official in statements at the Carnegie Endowment for International Peace in Washington on Thursday.
He also said the group is garnering wealth at an alarmingly quick pace, with large chunks coming from black-market oil sales and ransom payments for hostages.
"To some extent, It poses a different terrorist financing challenge," he said.
"It has amassed wealth at an unprecedented pace, and its revenue sources have a different composition from those of many other terrorist organizations" he said.
Cohen said the Treasury Department would target with sanctions anyone who deals with Daesh stolen oil.