The volume of gas accumulated by Ukraine in underground gas storage facilities (UGS) as of the end of September amounted to 13.9 billion cubic meters (bcm), head of Naftogaz Yuriy Vitrenko said. "Now we already have 13.9 billion cubic meters of gas. This will allow us to confidently enter the heating season. We will continue to monitor," he said at a briefing in Zhytomyr region.