Plummeting fuel prices and battlefield losses have forced the Islamic State to slash payroll, reports CNN Money.

FILE - In this June 16, 2014 file photo, demonstrators chant pro-Islamic State group slogans as they carry the group's flags in front of the provincial government headquarters in Mosul, Iraq. Under its leader, Iraqi jihadi Abu Bakr al-Baghdadi, the Islamic State group top command is dominated by former officers from Saddam Hussein's military and intelligence agencies, according to senior Iraqi officers and top intelligence officials. (AP Photo, File)

Credit: George Mathis

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Credit: George Mathis

Recently, the U.S. bombed a bank containing millions in cash used to pay ISIS troops, but the real blow has come from the collapsing oil market. Oil that cost $105 a barrel in June 2014, when ISIS invaded northern Iraq from Syria, now sells for less than $30.

Paying less for gas has never felt better.

ISIS troops, who are paid as much as $1,200 a month, now make less than U.S. Army privates, who make about $1,600 a month according to my math. Some ISIS regulars are paid as little as $400 a month, but, as we will see below, many augment their salary by looting and extorting those unfortunate enough to live in terrorist-controlled areas.

ISIS now makes most of its money by taxing 8 million or so residents of seized areas, including thousands of square miles in northern Iraq once under the control of the U.S. military. ISIS also has a significant presence in Libya, another oil producing country bombed by the U.S.

In 2014, the terrorist organization was pulling in $2 billion a year in total revenue , but half of that came from the one-time looting of Iraqi banks. It's estimated the terrorist group made up to $1 billion in 2014 by stealing cash and gold from government-owned banks. ISIS generally leaves private banks untouched and taxes residents on withdrawals.

Taxes, in 2014 accounted for almost $400 million in revenue.

ISIS charges a 10 percent income tax and 2 percent sales tax. Bank withdrawals are taxed 5 percent and drugs carry a tax up to 35 percent. Residents, young and old, are also extorted for cash. Schoolchildren in ISIS areas must pay an additional $22 to $45 a month to attend school, university students $65.

Troops on major roads charge up to $1,000 to let a vehicle pass.

Christians are forced to pay for mafia-like protection services called "jizyah." I could not find good numbers on what such insurance costs, but some estimates said Christians pay about $1,000 a year to not be murdered for their beliefs.

Oil, in 2014, accounted for about $500 million a year in revenue. ISIS sells oil to anyone who will break international restrictions on buying it, including its enemies in Syria and allegedly Turkey, a NATO ally.

Kidnappings made ISIS an estimated $40 million in 2014. Most of those kidnapped are local Christians or other non-Muslims. Hundreds of Assyrian Christians were kidnapped in 2015 and some were released for a ransom of $1,700 each.