The interest in measuring energy security results not only from its rising prominence but also from is increasing complexity. In the past, energy security concerns were no less acute than they are today. Consider, for example, the importance of access to oil for nations engaged in major wars of the 20th century. Yet, to strive for energy security in such cases did not require complex measures because policy makers were directly engaged and closely familiar with these immediate and pressing issues. In contrast, today's energy security problems often overlap national, institutional and sectoral boundaries stretching the cognitive abilities of experts and policy makers to deal with diverse situations and challenges which may not be directly familiar or predictable. One approach to cutting through this complexity is relating energy security to a common yardstick that would allow comparing it across different countries, at different points in time or to other policy priorities, in other words quantitatively measuring energy security. The challenge of measuring energy security is not only to see through natural, technological, and economic complexities and uncertainties, but also to address the fact that it has different meanings or different groups (Chester, 2009)