The Russian consortium is made up of state oil company OAO Rosneft, Transneft, and a subsidiary of state-controlled gas giant OAO Gazprom.
They will be responsible for the infrastructure, pumping stations, storage facilities and loading docks.
Claudia Kemfert, an analyst at the German Institute for Economic Research, said: "Russia already provides Europe with a third of its oil and 40 per cent of its natural gas.
"You get a strengthening of supply, but it can create higher dependency and other problems. You always have a trade-off ... to avoid this we need more diversification on the supply side, and to be less dependent on Russian energy," Kemfert said.
"We need to look more to the global market ... but pipelines are not that flexible."
The 90cm (36-inch) diameter pipeline will channel 700,000 barrels of oil a day to Greece, and have a potential capacity of 1 million barrels.
On Monday, Matthew Bryza, US deputy assistant secretary of state for European and Eurasian affairs, visited Athens and expressed support for the project.
But he said: "Where we are focusing most urgently now is diversification of gas supply ... away from its one primary supplier, Gazprom."
US officials want Greece to prioritise gas from Azerbaijan in a natural gas network being built from central Asia to Greece through Turkey that is due to continue onto Italy after 2011.
In Athens, 3,000 police have been deployed for Putin's visit, which coincides with plans for a mass student demonstration in the Greek capital on Thursday.