The objective of this paper is to briefly review the existing concepts of energy supply security in the context of the Security of Gas and Electricity Supply in Central and South-East Europe project. Based on this survey we are to propose a set of security of supply (SoS) measures that could regularly be quantified and compared for various regions, across countries and over time. Such comparisons will hopefully contribute to the evaluation of changes in regional energy supply security that might be of interest for private investors as well as policy makers.