The Bulgarian government said South Stream was given national priority status, eliminating legal, tax and other obstacles to the pipeline's construction through the country, the Internet news magazine New Europe reports.
Sofia, the report adds, said it was moving in step with regional ambitions to add diversity to the regional energy sector and enhance energy security.
Conventional natural gas transit options through Ukraine are risky for Europe given past political acrimony between Moscow and Kiev. About 20 percent of European gas is moved from Russia though 80 percent of that runs through Soviet-era pipelines in Ukraine.
Sofia in June said it expected that Azerbaijan will start shipping natural gas in some form to the country by 2014, possibly through the 2,000-mile South Stream rival Nabucco.
New Europe notes Sofia's commitment to South Stream has depended on the make-up of the government. It adds that Russian energy company Gazprom was last month forced to deny media reports it was planning to build South Stream around Bulgaria.
Sofia last week walked away from the planned Burgas-Alexandroupolis oil pipeline, which includes Gazprom as a consortium member, after years of political wrangling.