MOSCOW, August 29 (RAPSI) – An arbitral tribunal is expected to issue a decision in the dispute between Naftogaz and Gazprom over gas deliveries in mid-2015, EU energy commissioner Günther H. Oettinger said on Friday.

The companies commenced arbitration proceedings against each other under the Stockholm Chamber of Commerce rules in June. Naftogaz claims that it has been overcharged by the Russian company. Gazprom says that Naftogaz has failed to pay $4.5 billion for gas that has already been delivered.

Gas talks between Russia, Ukraine and the European Union went on from April to mid-June. Kiev said it would not repay its debt unless Russia agreed to supply gas at a lower price.

The proceedings were invoked after Gazprom switched to a prepayment system for gas deliveries to Ukraine on June 16.