Brussels says the South Stream gas pipeline can still go ahead.
Russia had scrapped the 400 billion euro project to pump gas to the European Union, citing legal obstacles as a reason.
It would have bypassed Ukraine, the traditional transit route for Russian gas, The first point for the pipeline in the EU would be Bulgaria.
Some EU nations, especially Bulgaria, which is almost entirely dependent on Russia for its gas and would stand to benefit from a pipeline via its territory, are strong supporters of the Gazprom project.
On Thursday European Commission President Jean-Claude Juncker had talks in Brussels with Bulgarian Prime Minister Boyko Borisov.
“South Stream can be built. The conditions have been clear since a long time … There is nothing new. The ball is in the court of Russia,” said Juncker.
Borisov also said South Stream had to comply with EU rules, including legislation, known as the third energy package, that limits how much of a pipeline a company can own if it also controls the gas supply.
“We want “South Stream” to be built, respecting European rules,” he said. “On 9th December in Brussels will decide exactly how to implement these European rules.”
Further efforts to bring the project in line will be made on Tuesday, when EU energy ministers are in Brussels for regular talks.