If this is true, then why does ISIS get into financial trouble only now? The airstrikes in Syria have been going on already since September 2014. Did the USA realize that they should start bombing oil transports only recently?
On the other hand, Russia has claimed to have been bombing oil transports since the very start of their air campaign. Which happens to have started a couple of month ago. Maybe I'm too suspicious, but to me it looks like ISIS is getting into trouble because of the recent Russian intervention, and not because the USA.