To achieve sustainable development goals (SDGs), it is necessary to solve the problem of assessing and measuring energy sustainability performance. A popular indicator used for this purpose is the World Energy Council (WEC) energy sustainability index, or the Energy Trilemma Index, which is based on such key metrics as energy security, energy equity, environmental sustainability, and country context. Each of the four metrics, or dimensions, includes many indicators that depend on both internal and external factors. By combining a variety of indicators into integral ones, WEC ranks countries in terms of energy sustainability. However, what is not taken into account is how countries differ in terms of economic development, income, energy mix, renewables use, ownership in the energy sector, and other factors, and neither is the methodology itself disclosed by the developers. As a provider for all other sectors of the economy, the energy sector plays an important role in developing countries. Ecuador, Colombia, Peru, and Bolivia, being members of the Andean Community, are neighbors and have similar economic conditions but lack transnational power grid interconnections, which hinders the development of a common energy market. In terms of energy sustainability, these countries’ ranks range from 45 to 101, according to the Energy Trilemma Index. The aim of the study is to develop a new methodology for assessing energy sustainability performance that will factor in the specific features of developing countries with a high share of hydroelectricity generation, and to calculate energy sustainability index indicators taking into account contemporary requirements for sustainable development, which include developing green and renewable energy and fostering decarbonization. This research reveals whether the countries’ energy sustainability indices correspond to their actual performance in energy development and identifies the factors influencing the values of the metrics in the Energy Trilemma Index. The methodology can be used to integrate the energy sectors of countries, as it allows for evaluating the state of the energy sector of several countries (for example, those of the Andean Community) as a whole.