„Various Israeli assessments say that the organization that calls itself the Islamic State of Iraq and the Levant – Islamic State for short – has lost more than one-third of its fighting members over the past 18 months. Israeli and other Western officials estimated the number of its combat fighters at roughly 25,000 in early 2015. The current estimate stands at approximately 15,000. (…)
The flow of volunteers has all but stopped. This, too, seems to be linked to several factors, such as Turkey’s military intervention on Syrian territory last month, which has made it difficult for volunteers to get through; the first battlefield defeats in major cities such as Fallujah, Ramadi, Minbaj, and Palmyra, which hurt Islamic State’s image as an undefeated power; and more strenuous efforts by European countries against Islamist groups. Contributing to these difficulties and in part caused by them, Islamic State itself now asks its supporters abroad to remain in their countries of origin and act there against ‚the kuffar [infidel].‘
The group has also seen a dramatic decline in income. Its revenue in 2015 from its crude-oil industry was estimated at $600-$700 million. The current prevailing estimate is that this pace of income has been cut in half, with crude oil revenues for 2016 expected to be roughly $250-$350 million. If revenue from crude oil made up half of Islamic State’s income in 2015, it currently comprises only one-third of its income.“
(Avi Issacharoff schreibt für The Times of Israel: „Israel believes Islamic State has lost 10,000 fighters in past 18 months“.)