Islamic State is still extracting and selling oil in Syria and has adapted its trading techniques despite a month of strikes by US-led forces aimed at cutting off this major source of income for the group, residents, oil executives and traders say.
While the raids by US and Arab forces have targeted some small makeshift oil refineries run by locals in eastern areas controlled by Islamic State, they have avoided the wells the group controls.
This has limited the effectiveness of the campaign and means the militants are able to profit from crude sales of up to $2 million a day, according to oil workers in Syria, former oil executives and energy experts.
"They are in fact still selling the oil and even stepping up exploitation of new wells by tribal allies and taking advantage of the inability of the enemy to hit the oil fields," said Abdullah al-Jadaan, a tribal elder in Shuhail, a town in Syria's oil-producing Deir al-Zor province.
US-led forces want to avoid hitting the oil installations hard because it could hurt civilians more than the militants and could radicalise the local population, analysts say.
On Thursday the United States threatened to impose sanctions on anyone buying oil from Islamic State militants in an effort to disrupt what it said was a $1-million-a-day funding source.
Most of the oil is bought by local traders and covers the domestic needs of rebel-held areas in northern Syria. But some low-quality crude has been smuggled to Turkey where prices of over $350 a barrel, three times the local rate, have nurtured a lucrative cross-border trade.
"Our options are limited unless you hit the wells - but it does not just hit Islamic State, it hits the entire population and that is not something that the US can do very easily," said Andrew Tabler, a senior fellow at the US-based Washington Institute, who focuses on Syria.
"It's a good example of the constraints of trying to bomb your way out of it."
Any bombing of Syria's major oil wells could evoke memories of the 1990-1991 Gulf War when the forces of Iraq's Saddam Hussein invaded Kuwait and burnt oil wells as they were repelled by US-led forces, causing severe damage to the infrastructure.
