DUBAI: Though the dreaded Islamic State is earning over $3 million daily by producing about 80,000 barrels of oil in Iraq and Syria, experts say the group is finding it difficult to maintain its gains and emerge as an energy player.

The Islamic State (IS) extremist group popped up on the global radar in June by seizing assets in Iraq, but building on those early gains, according to a number of energy sources, is proving difficult.

August was not a good month for IS, CNN quoted experts as saying.

It lost its battle for one of Iraq's biggest oil fields in Kirkuk, with potential production of 600,000 barrels a day, and could not keep control of Iraq's largest refinery at Baiji.

What the militants do hold, Iraqi officials say, will need regular maintenance. So far, it is getting that work done only through intimidation of on-site engineers who are not loyal to the IS cause.

IS's income from oil is falling as they struggle to control the personnel within refineries, Assim Jihad, a spokesman at Iraq's oil ministry, said.

"At first they got a large sum of money by seizing inventories, but this cannot last," he said.

The Iraq Energy Institute estimates IS is producing about 30,000 barrels a day in Iraq and 50,000 daily in Syria. On a black market price of $40 a barrel, it is earning $1.2 million a day in Iraq and $2 million in Syria.

Energy traders and regional security specialists say supplies are being funneled into regional oil importing countries of Jordan, Turkey, and Syria.

"They use oil tank trucks instead of oil pipes. There are about 210 oil tank trucks smuggling oil to Turkey and other places every day," Hussein Allawi, senior consultant at Iraq's oil ministry said.

While IS has clearly suffered setbacks, there is also a stark reality.

The organisation may be falling short of designs to become a "state" oil company, but revenue of over $3 million a day can certainly finance its operation of terror.

The IS group has carved out a self-styled caliphate in the large area along the Iraqi-Syrian border that it now controls.

World leaders, including US President Barack Obama and British Prime Minister David Cameron have vowed that they will "not be cowed" by IS extremists who have killed two American journalists in as many weeks.