Measuring the performance of the energy system of a country is a prerequisite for framing good energy polices. However, the existing indices which claim to measure energy security have limited applicability for developing countries. Energy sustainability is also increasingly gaining importance and countries are keen to measure it to tailor their energy policies. Therefore, the concept of SES (sustainable energy security) has been proposed as the goal for a developing country. This paper presents an analytical framework for the assessment of SES of an energy system and the methodology for constructing an SES index. A hierarchical structure has been proposed and the energy system has been divided into 'supply', 'conversion & distribution' and 'demand' sub-systems. Each subsystem is further divided into its components which are evaluated for four dimensions of SES, Availability, Affordability, Efficiency and (Environmental) Acceptability using quantitative metrics. Energy indices are constructed using 'scores' (objective values), and 'weights' (subjective values representing tradeoffs) which are then aggregated, bottom-up, to obtain an overall SES Index for a country. The proposed SES Index is multidimensional, quantitative, modular, systemic and flexible. Such a SES Index can be used to design policy interventions for transitioning to a sustainable and a secure energy future. (C) 2015 Elsevier Ltd. All rights reserved.