The article argues that despite the evident link between political environment and security of energy supply, political elements are not sufficiently represented in contemporary scientific literature, namely in indexes that are designed for the assessment of security of energy supply. In an attempt to fill this gap, the article presents an innovative methodology for quantitative assessment of the political vulnerabilities on security of energy supply and applies it to the analysis of the Baltic States. The proposed index determines the plausibility of the occurrence of threats of a political nature on the security of energy supply and defines it as political vulnerability. The application of index methodology to an analysis of the Baltic States has revealed that the overall political vulnerability on security of energy supply is the highest in Lithuania, considerably lower in Latvia, and the lowest in Estonia. The analysis has shown that political vulnerability has increased in Lithuania due to the closure of Ignalina NPP and an increase in energy import quantities from politically unstable countries, such as Russia. On the contrary, political vulnerabilities on the security of the energy supply have decreased in Latvia and Estonia due to the increase of consumption of indigenous energy. However, preliminary calculations show that political vulnerabilities should decrease considerably in 2015 in Lithuania due to the diversification of the natural gas supply.