Gazprom said a South Stream planning company and Siemens entered into a contract for the electrical system of the offshore section of the pipeline.
"The document stipulates that Siemens will supply telecommunication equipment and automatic process control systems for the Russian and Bulgarian landfalls," Gazprom said in a statement.
No value of the contract was outlined and there was no statement Friday from Siemens.
Gazprom said the offshore section of South Stream will consist of four parallel lines running about 575 miles across the Black Sea.
The Russian natural gas company said it plans to commission parts of South Stream before the end of 2015. The pipeline is designed to have an annual capacity of 2.2 trillion cubic feet and is part of a regional effort to avoid geopolitically sensitive territory in Ukraine.
European leaders have said they were reluctant to embrace the project given the political conflicts that erupted in the wake of Russia's decision to annex Crimea, a peninsula of Ukraine.