Gazprom's gas exports to Europe fell almost 12 percent in January-July to 82.2 billion cubic metres from export levels in the same period a year ago.
Gazprom, which covers over a quarter of Europe's gas needs, expects to export 150 bcm of gas to the European Union this year, unchanged from 2011.
But output slumped almost 11 percent in July, and it faces competition from cheaper gas on the spot market.
The source also said the average Russian gas price in Europe stood at $400 per 1,000 cubic metres for the past two months. Gazprom sees average 2012 gas price for the EU at between $405 and $415 per 1,000 cubic metres, up from $390 in 2011.