This report presents the findings of a study aiming to define the least cost short (up to 2015) and medium term (up to 2020) measures that the Government of Bulgaria (GoB) can implement to meet gas security of supply requirements seen in the light of Bulgaria's vulnerability to gas supply disruptions and its increasingly important role for regional gas cross-border transmission and trade. Bulgarian gas demand is of modest size (3.0 bcm in 2011) and natural gas only plays a small role in Bulgaria's energy mix (14 percent of the total primary energy supply). Over the next ten years gas demand patterns are likely to change, however, and consumption levels are expected to grow steadily. The growth rate of gas demand and its importance in the supply mix will be driven by choices of electricity generation strategy and the rate of household gasification. There is a significant risk that a gas-focused electricity strategy would reduce Bulgaria's overall security of supply. However, this would only be the case if the new gas supply was contracted from the same sources and routes as the existing contracts (from Russia via Ukraine) and if the gas-fired power plants did not have back-up fuels. Conversely, if Bulgaria is able to secure new gas contracts from other sources delivered via new routes, and if back-up fuels are provided at those plants, then Bulgaria could increase its gas consumption while increasing its overall energy security of supply. This issue is at the core of the present report.