In 2015, the OPEC countries recorded their lowest revenues since 2004. The Energy Information Administration (EIA) declared so in one of its recent reports.
Specifically, last year OPEC countries earned $404 billion from net exportations of oil, -46% in comparison to the $753 billion in 2014. And the report also considers Iran's new revenue, after the end of sanctions.
More generally, according to the EIA, the earnings of the individual countries have been affected above all by the drop in the price per barrel, which went from $112 in December 2014 to $38 in the same period last year. And 2016 will not go any better. The EIA estimates that revenues will drop to $341 billion, and then go back up to $427 billion in 2017, still some way off the figure reached 2 years ago.