U.S. intelligence officials revealed last week that they believe the Islamic State, also known as ISIS, is reaping as much as $3 million a day in revenue, making it one of the wealthiest terrorist groups in history.
The group desperately needs the money, for as one U.S. official recently told NBC: "Running a caliphate is not cheap." ISIS needs to pay, arm and feed its brigades. The group also rewards the families of killed militants with a pension, and it needs to cover the costs of governing the territory it has captured.
This is where the Islamic State is getting its money from:
1. WEALTHY DONORS
Just like other radical militant groups fighting in Syria, the Islamic State initially relied largely on cash gifts from wealthy sympathizers who were determined to support Sunni fighters in their revolt against Syrian President Bashar Assad.
Much of the fundraising for Syria's extremist groups occurs in the Arab Gulf states, where wealthy private donors raise millions to hand over to Islamist fighters at the Turkey-Syria border. The governments of Saudi Arabia, Qatar and Kuwait also covertly provide millions in aid to radical Sunni groups fighting Assad.
Since it launched a massive offensive in Iraq in June, the Islamic State has managed to capture a stretch of territory in Iraq and Syria that's about the size of the U.K. The militants were able to steal millions of dollars in cash and other materials from banks and military installations during its campaign, according to the Associated Press.
The Islamic State also levies taxes in the areas it conquers. The Council on Foreign Relations estimates that the group was netting more than $8 million a month in taxes from small and large businesses even before capturing Mosul, Iraq's second largest city, in June.
Oil appears to be the largest source of income for the Islamic State today. The militants pump crude oil from about a dozen oil fields they have captured in Syria and Iraq. They either sell the crude oil directly or send it to small refineries to produce low-quality fuels. It is then transported via decades-old smuggling routes over the border and sold at low prices on the black market in Turkey and in smaller volumes to the Syrian regime.
The Islamic State is also believed to have made millions from human trafficking and ransom extortion. Al-Khatteeb told the Associated Press that the group is selling some women and children it kidnapped as slaves.
The militants have also brought in millions in ransom paid by the relatives and governments of some hostages. While the U.S. and Britain have publicly said they refuse to pay for the release of their citizens, several European governments have paid millions to captors. U.S. officials recently told NBC that they believe some European countries have paid seven-figure ransoms.