[Mariner]

" Russia has been overcharging the Ukraine and failed to fulfill its contractual obligation to make the required deliveries called for in the contract. Russia owes the Ukraine upwards of $15 billion in overpayments, and not the other way around."

OK, I'm interested.

Is there a non-Ukrainian source for that contention?

[WhiskeyX]

"Is there a non-Ukrainian source for that contention?" As of October 2013 Lithuania, Poland, Ukraine, and perhaps others were taking action against Gazprom for overcharging by billions of dollars. One of the sources for these stories is the official Russian government controlled news agency. Their complaints like that of the Ukraine today were being taken to a Swedish venue for a resolution. See the new post: Lithuania wants Gazprom to pay back $1.5 billion it has overpaid ITAR-TASS News Agency ^ | October 04, 13:09 | Russian Press Review Posted on ‎5‎/‎8‎/‎2014‎ ‎9‎:‎14‎:‎34‎ ‎PM by WhiskeyX