No single set of metrics is suitable for assessing energy security for all purposes in all situations for these country groups. Table 2.2 outlines important factors contributing to energy insecurity of a nation, region or particular group of countries. Energy security in this framework is defined as low vulnerability of vital energy systems. The vulnerability of a system is the degree to which that system is unable to cope with selected adverse events. Such a framework allows review of security of vital energy’ systems from the perspectives of such criteria as criticality, likelihood of the event, and level and type of damage.