The deal, signed by Russian Energy Minister Sergei Shmatko and Slovenian Economy Minister Matej Lahovnik, will ensure Slovenia’s participation in the project.
“We have now signed deals with all the European partners needed for this project to be completed,” Putin told reporters at his Novo-Ogaryovo residency outside Moscow after signing the co-operation deal with Slovenian counterpart Borut Pahor.
Gazprom has already made agreements regarding South Stream with Bulgarian, Greek and Serbian energy companies. Mr Putin has also invited Austria to join the project but a final response has not yet been given.
With a capacity of 63 Bcm/a, the South Stream Pipeline will deliver gas from Russia and Central Asia to Europe via the Black Sea.
The pipeline is expected to cost between $US28-36 billion and is planned to become operational in 2015.