Chevron secured the rights to explore the Novi Pazar shale gas deposit in Bulgaria, beating out Canadian rival BNK in the bid, the country's Energy Ministry said.
Bidders had estimated the field has 1.05 trillion-35 trillion cubic feet of natural gas deposits.
Chevron assumes the risks associated with the field, including whether sufficient quantities of natural gas will be discovered and whether exploration plans will get a positive environmental assessment, the Sofia News Agency reports.
Shale gas is emerging as a key natural resource in countries like the United States and Poland. Extraction methods, known as fracking, are controversial because of the perceived potential of groundwater contamination.
Bulgarian Energy Minister Traicho Traikov said there is potentially enough shale gas in the deposit to meet domestic demand for the next millennium.