Russia on Friday agreed with three major European energy firms to build a natural gas pipeline across the Black Sea as part of an ongoing Kremlin strategy to diversify export routes westward and bypass Ukraine, dpa reported.Russian Prime Minister Vladimir Putin was at the signing ceremony in the Black Sea resort city of Sochi, along with the heads of France's EDF, Italy's Eni, and Germany's Wintershall.Russia's natural gas monopoly Gazprom will take a 50 per cent stake in the offshore section of South Stream pipeline project, with Eni receiving 20 per cent and EDF and Wintershall each receiving 15 per cent.South Stream plans a 900-kilometre pipeline connecting Russia's Black Sea port terminal Dzhubga with the Bulgarian city of Varna. Its maximum capacity is rated at 63 billion cubic metres a year, or roughly 10 per cent of current total EU consumption.The undersea section of the line should be operational in 2015, a statement from the South Stream company said.Balkan branches of the South Stream pipeline willcarry Russian gas onward to Italy and Central Europe. Onshore sections of the pipeline will be built by local joint ventures between Gazprom and energy companies in Austria, Bulgaria, Croatia, Greece, Hungary, Serbia and Slovenia, the statement said. Gazprom officials have long supported an under-the-Black Sea gas delivery route as a way of preventing possible Ukrainian interference with Russian natural gas deliveries to Europe. Deliveries of Russian natural gas to Europe saw stoppages in 2006 and 2009 because of disputes between Gazprom and Ukraine over natural gas pricing. Currently, some 80 per cent of all Russian gas exported to Europe reaches market via pipelines crossing Ukraine.Russia in early September began pumping gas into a trans-Baltic Sea pipeline called North Stream which, once operational in October, will deliver Russian natural gas directly to Germany.