The daring overnight commando raid on senior ISIS leader Abu Sayyaf's lair puts a spotlight on the importance of the terrorist group's finances from oil and gas — and how uniquely critical that black market money is to the network's survival.
And for the U.S. to stomp out ISIS, taking down its financing appears just as important as taking out the group's operations in air attacks. Sayyaf was charged with directing ISIS's oil, gas and financial operations, and his death in Friday's U.S.-led mission could potentially puncture those funding sources.
There are other sources of money for the group, such as extortion and ransom (and to a lesser degree donations and "taxes"), but oil and gas are seen as the most vulnerable to U.S. military action.
Counterterrorism officials both inside and outside the U.S. government say ISIS is all about holding territory, which is expensive, rather than carrying out terrorist attacks, which is not.
A U.S. counterterrorism official told NBC News recently that encouraging attacks by "fan boys" in places like Paris and Tunis allows ISIS to reap cheap publicity without expending the precious revenues needed to protect its caliphate in Iraq and Syria.
All that the terror attacks require, said the official, "is an idea and a hashtag."
"I am not sure they are really achieving anything by these very infrequent one-off attacks," said Michael Sheehan of the Combating Terrorism Center at West Point. "They are in the news for a few days and life goes on."
Sheehan believes the real threat posed by ISIS is the attraction of the caliphate — an Islamic utopia spreading across the Middle East — and that needs money, hundreds of thousands of dollars a day. And ISIS is paying not just its fighters and the families of fallen "martyrs," but the clerks who run the municipal government in Mosul, a city of 2 million under its control for a year.
As a result, the money is going out as fast as it's coming in, according to U.S. intelligence. Oil and refined gasoline are also important, of course, to ISIS military operations.
That's why Abu Sayyaf was so important. A U.S. military official identified Abu Sayyaf as the "emir" of ISIS oil and gas operations, which has been one of ISIS's most successful financial resources.
He was unintentionally killed in the U.S. Special Operations Forces raid in Deir ez-Zur in eastern Syria, near ISIS-controlled oil fields and refineries, the White House said.
As one U.S. military official told NBC News, there were four "primary purposes" in the raid: To capture Abu Sayyaf as well as his wife, Umm Sayyaf; free the a young Yezidi slave being held in the compound; and to gather intelligence about ISIS's finances, management and operations.
"We accomplished 3 of 4 purposes and justice was still served with Abu Sayyaf," the military official said.
IIlicit oil and gas sales through Turkey are seen as the second-biggest source of ISIS financing, after the hundreds of millions of dollars in currency, gold and financial instruments seized from the Central Bank of Iraq and other banks last June.
When ISIS took control of large swaths of Syria and Iraq last summer, the International Energy Agency estimated it had access to 3 million barrels of oil and could ship up to 70,000 barrels a day, most of it in older fields in eastern Syria.
Both those numbers have been reduced dramatically by airstrikes from the U.S., Saudi Arabia and the United Arab Emirates, say U.S. and International Energy Agency sources.
Recent strikes have targeted the terror group's oil storage depots and makeshift refineries. As a result, says the IEA, the amount of oil shipped dropped to 20,000 barrels per day. Turkish authorities have also begun stopping oil shipments across the border, although the U.S. would like to see more action by the Turkish government.
The volatility in world oil prices has also undercut the ISIS strategy of selling oil at far below the going rate.
Last year, ISIS was believed to be selling oil on the black market for as little as $25 a barrel, which was then one-quarter of the market price. But when the price per barrel dropped to less than $50 earlier this year, ISIS oil becomes less attractive to rogue traders.
"They have difficulty in moving product and the oil, mostly crude, is lousy," said one U.S. government analyst.
But with oil prices rising as of late, there's always the possibility of ISIS getting back to previous levels. Moreover, IEA officials have said, the group could be expected to gain access to other additional sources of fuel.