The Shtokman field to Murmansk

Quoting a source close to the talks, the Russian news agency says the French bank Calyon has been chosen, knocking HSBC and BNP Paribas out of the race.

Calyon would join a Russian project finance bank and the in-house bank Gazprombank to advise on the project.

The giant Shtokman natural gas deposit could be worth up to $20bn.

Gazprom, which is already the world's largest gas producer, is about to start pumping gas from the hitherto unexploited field, in the Russian parts of the Barents Sea.

Mr Medvedev says Shtokman is one of Gazprom's biggest project

Gazprom has invited foreign oil companies to pitch for participation in a consortium that should be ready by 1 April to start developing the strategically crucial field, 555 kilometres north-east of Murmansk on the Kola peninsula.

The 1,400 square kilometre field is set to become the world's largest offshore gas field with 3.2 trillion cubic metres of gas contained in reservoirs two kilometres below the seabed, which is itself at a depth of 350 metres.

"The Shtokman field is one of Gazprom's most significant projects in the next five years," Gazprom's deputy chairman Alexander Medvedev told BBC News in a recent interview.

"It is a unique field, with unique reserves.

"If all goes according to plan, the field should be ready by 2010."