Income and population figures in the so-called 'Islamic State' have declined dramatically since the middle of last year according to new research.
The latest publication from US analysis firm IHS says that the self-proclaimed caliphate's monthly revenue has fallen from close to $80m in the middle of last year to $56m per month in March.
Its daily oil output has dropped from 33,000 barrels to 21,000 barrels, as a number of production facilities were hit during air strikes.
The total area controlled by the Sunni Muslim group has fallen by 22% while its population has declined by a third, shrinking from 9 million to 6 million.
The report adds that the group has begun taking cash payments to pardon condemned prisoners, it has also introduced a series of new taxes on activities such as satellite dish installation and leaving city boundaries to help to bring in extra income.
IHS senior analyst Ludovico Carlino commented: "Islamic State is still a force in the region, but this drop in revenue is a significant figure and will increase the challenge for the group to run its territory in the long term."
