In late 2017 the World Bank released a study of ISIL (Islamic State in Iraq and the Levant) finances from 2014 to 2017 and revealed some of the techniques used to measure how much oil the terrorist organization obtained over three years of using captured Syrian and Iraqi oil fields. It was known since mid-2014 that this was going on. That’s because by mid-2014 ISIL was trying to clear all opposition out of their stronghold in eastern Syria. It quickly became clear that this was mainly about money and as ISIL gained control over most of the oil fields in eastern Syria and several in northern Iraq. They strove to capture them undamaged and had already recruited people who could keep the fields operating. The oil was sold to smugglers, at a big discount, and the smugglers then trucked it into Turkey or Kurdish areas and sold it to brokers who buy oil with no questions asked.
The World Bank described the simple methodology used to measure this activity. It was based on using commercial surveillance satellites that regularly provided pictures of the area. This showed how much natural gas was being burned (“flared”) at the wells as the oil was produced. This is a common practice in many oil fields and there was much data on how much flared gas accompanied how much oil being produced.
As commercial satellite data became cheaper and regularly available since the 1990s this became a common method of measuring how much oil was actually being produced worldwide. Economists and anyone monitoring actual production had access to this data. Thus it was known that the ISIL controlled oil fields were producing about 56,000 BPD (barrels per day) during the last six months of 2014. Coalition air attacks reduced that to 35,000 BPD during 2015 and 16,000 BPD in 2016. That rapidly dropped during the first few months of 2017. How much ISIL received per barrel from the brokers and smugglers became known gradually as information could be extracted from those sources. It apparently averaged about $25 per barrel meaning that ISIL obtained about $40-45 million a month in 2014 from this source. In 2015 that fell to $20-30 million and in 2016 it was $10-15 million in 2016. In 2017 it was down to $5 million or less per month and this decline was verified by ISIL prisoners, defectors and deserters through that period as well as data provided by civilians escaping ISIL controlled territory as well as those few who managed to use cell phones or Internet access to communicate from ISIL territory in that period. The reduced income meant ISIL could not pay its personnel or buy essential supplies from smugglers. These economic woes played a major role in ISIL losing control of the territory it ruled during that period.
The Americans knew ISIL had a cash vulnerability because they had confronted this situation before in Iraq. Thus it was not mystery why ISIL maintained control of large chunks of Iraq and Syria for over two years. It was because they paid attention to logistics (getting supplies) and finance (finding ways to pay for the supplies.) ISIL succeeded because they had plenty of qualified and experienced administrators willing and able to get the job done.
This came about because for centuries the Sunni minority in what is now Iraq ran the largely Shia area. For most of the last four centuries the area was part of the Turkish Ottoman Empire. The Sunni Turks had taken what is now modern Iraq from Shia Iran and did not trust the Shia Arabs to run things. The Sunni Arab minority in the area was another matter as this group was always better educated and more prosperous than the Shias and tended to run Baghdad and areas to the south no matter what empire was in charge. So the Turks had these Sunni Arabs administer this part of their empire. When the Ottoman Empire fell in 1918 the British took over, looked around and decided to leave the Sunni Arabs in charge. In 1932 Iraq became independent as a constitutional monarchy but the king, most army officers and senior officials were Sunni Arabs and largely controlled the new Iraq.
The British had to re-occupy Iraq during World War II because the Sunni Arab government tried to ally itself with the Nazis. At the time many Arabs admired Nazism (and many still do). The Brits again conquered the country, gathered together another bunch of Sunni Arab notables and told them they could run things if they stayed away from the Nazis. That 1941 deal lasted until the 1958 when the Sunni Arab politicians and generals decided that this constitutional democracy stuff wasn’t working for them. The royal family was massacred and parliament purged of “disloyal” elements. The Sunni Arabs were now firmly in charge, via a series of dictators, until Saddam Hussein was deposed in 2003. Despite the subsequent elections many in Iraq, not just the Sunni Arabs, believed a dictatorship (with them running it) would be the best solution for the nation's ills. Some Iraqis (mostly Sunni Arabs but even a few Shia Arabs) still admire Saddam and consider his blood-soaked reign a "golden age." Few Iraqi Kurds (who are Sunni) or Shia Iraqis agree with that.
When the American and British removed the Sunnis Arabs from power in 2003 many of the Sunni Arabs still believed they were born to rule and enjoy 80 percent of the oil wealth. That was a sweet deal since Sunni Arabs were only 20 percent of the population while Shia Arbs were 60 percent and other minorities (mostly Kurds) the rest. Al Qaeda came in after 2003 and added Islamic radical terrorists to all those terrorists that the Sunni Arab nationalists and Saddam supporters had recruited to help them put Sunnis back in charge. This backfired, as al Qaeda represented a form of political action that the post–World War II Sunni Arabs had abandoned and even gone to war with. Islamic radicalism was never all that popular in Iraq. But now, in the name of restoring Sunni rule Islamic terrorists were allowed to do as they pleased. This led to all non-Sunni Arabs becoming "legitimate targets" that could all be killed or driven out of the country. Such threats are nothing new and have been getting worse for over a century. Thus the old (founded in 2006) Islamic State of Iraq (which eventually became ISIL in 2013) still has a lot of veteran personnel who are fighting to get the Sunni Arab minority back in charge of Iraq at any cost. That effort was crushed by 2008 but the corrupt Shia government forced the Americans out in 2011 and, ignoring U.S. advice, froze out the Sunni Arabs and drove many right back to the Islamic terrorist groups. The Iraqi Sunnis made a comeback and were defeated again in 2017.
Yet ISIL still has that no other group had and that was access to thousands of trained and experienced Sunni Arab military officers, civil servants and technical specialists. This was long known but was confirmed again in early 2015 when an American commando raid into ISIL territory captured vast quantities of ISIL records (mostly on PC hard drives). An analysis of these documents clearly showed the presence of the Saddam’s henchmen who had set up a ruthless but efficient bureaucracy. Because ISIL was even less obliged to obey rules than Saddam they had a department of loot, which raised large amounts of money by selling slaves, oil and any valuable loot (like antiquities) ISIL captured. All that fund raising and administrative skill was not enough and now ISIL has most of the world united to destroy it. But mostly the Iraqi Sunni Arabs knew how to deal in oil, legally or otherwise. Thus the American efforts against ISIL after 2014 concentrated on the money and it worked for the second time in a decade.