Energy is one of the most important sectors for sustainable development of any country; however, its generation and consumption lead to environmental, economic, and social consequences, including climate change, pollution and energy poverty. Currently, there is much discussion and activity at the international level aimed at identifying sustainable energy options for the future. In an attempt to contribute to the debate in this area, the main objective of this research has been to develop a methodology to help assess the sustainability of energy systems with the view of identifying more sustainable energy options. The methodology has been applied to the energy system of Nigeria. However, the methodology is generic and can be applied to any energy system in any country.