BERLIN, Oct 2, 2008 (AFP) - The leading German energy group EON has reached an accord with Russian monopoly Gazprom to participate in the massive Siberian Yuzhno-Russkoye gas field, EON said on Thursday.

EON is to obtain a stake of 25 percent less one share in the operation, while Gazprom would recuperate a holding of 49 percent owned by EON in the Russian company ZAO Gerosgaz, the German group said.

ZAO Gerosgaz itself owns a 3.0 percent stake in Gazprom.

The transaction does not immediately affect a 3.5 percent stake in Gazprom already owned by EON, the company said.

The agreement was signed during a visit to Russia by German Chancellor Angela Merkel.

EON boss Wulf Bernotat said the deal would 'significantly reinforce EON's presence in the Russian energy market.'

The German group already owns the Russian electricity producer OGK-4.

'Gazprom and EON have shown again that they are long-term partners capable of cooperation along the entire chain of production,' Gazprom boss Alexey Miller was quoted as saying.

The Yuzhno-Russkoye field controls estimated natural gas reserves of more than 600 billion cubic meters (21 trillion cubic feet), which German press reports have said is enough to meet Germany's total gas needs for around seven years.

It was inaugurated in December 2007 by Dimitry Medvedev, now the Russian president, and German Foreign Minister Frank-Walter Steinmeier.