Bilateral disputes over gas contracts between Ukraine and Russian energy company Gazprom sparked concerns about European energy sector when, in 2009, the Russian side cut gas supplies to Ukraine briefly. That left downstream consumers in the cold as much of the region's gas supplies had traveled through the Soviet-era transit system in Ukraine.
European leaders have embraced a series of pipeline projects included in the so-called Southern Corridor to break Russia's grip on the regional energy sector. Gazprom, for its part, built the twin Nord Stream system through the Baltic Sea to Germany while advancing its South Stream network for southern Europe.
Gunther Oettinger, the energy commissioner for the European Union, told Bulgarian National Radio that he was intrigued by the Russian project.
"South Stream is a very interesting project, which the European Commission is ready to address constructively," he said.
Bulgaria this week become one of the last host country to agree to a final investment plan for the project. Gazprom said construction should begin next month and gas deliveries could start as early as 2015.