Oil production and smuggling in the Islamic State
Oil production and smuggling was the largest source of revenue for the finances of the Islamic State (IS or ISIS) in Syria and Iraq until the complete loss of its territory in 2019. Most oil extracted was distributed for use within the Islamic State, but some was also smuggled to surrounding states at below market price.
Source: Wikipedia — Oil production and smuggling in the Islamic State (CC BY-SA 4.0)