Very little analytical work had been published on the development of quantitative measurements of energy supply security. The objective of the NEA study was to identify approaches to measuring nuclear energy's contribution to the security of energy supplies and to quantify the risks associated with energy supply insecurity. The Ad hoc Expert Group on Nuclear Energy and Security of Supply, which had been formed to carry out the study, met for the first time on 22-23 November 2007 at OECD/NEA offices in Issy-les-Moulineaux, France. 20 experts from member countries and the French research institution Sciences Po who attended the meeting discussed possible qualitative and quantitative approaches to measuring the security of energy supply. They agreed that once the analytical approaches were identified, the expert group would assess nuclear energy's role in enhancing energy supply security. Five qualitative approaches were evaluated prior to the second meeting in June 2008, when quantitative techniques were sought and assessed. This allowed expert group members to compare qualitative and quantitative approaches, leading to an informed decision on the quantitative approach that would be used during the remainder of the study.