National joint-stock company Naftogaz Ukrainy continues negotiations with Russia's OJSC Gazprom on the possibility of buying gas in the third quarter of 2016, but the supplementary gas contract to the 2009 contracts that would allow Naftogaz Ukrainy to resume purchases of Russian gas has not yet been signed, Naftogaz Board Chairman Andriy Kobolev has said.

He said at a press conference in Kyiv on Thursday that European gas would be enough to fill underground gas storage facilities by Ukraine, and the issue of buying gas from Gazprom is only commercial.

"Gazprom's price is slightly lower than the price of European suppliers," Kobolev said.

He said that the market is volatile. Price falling trends are seen on the European markets, Kobolev said.

He confirmed the plan to enter the heating season with gas stocks of 14.5 billion cubic meters.

"These stocks could be accumulated without supplies from Gazprom," he said.

According to Gazprom's data, the price for Ukraine for the third quarter under the formula of the 2009 contract is $167.57 per 1,000 cubic meters, although taking into account its calorific capacity Kobolev assesses it at some $173 per 1,000 cubic meters.

Natural gas stocks in Ukraine's underground inventories after the 2015/16 heating season increased by 15.3% or 1.29 billion cubic meters, to 9.73 billion cubic meters.