Abstract : Pushed by the need for carbon emission abatement and the expected depletion of fossil fuels, electricity generation is entering a period of signicant change. At this point in time, the issue of integrating distributed and renewable energy sources puts a question mark over the future shape of the electricity industry. In this paper, we are interested in the level of reliability of future electricity mixes and whether or not these changes will impact the level of reliability. Consequently, we propose a methodology for assessing the reliability of power systems based on a number of aggregated physical properties. Finally, we exhibit “reliability indicators", which provide valuable comments on reliability using distributed and renewable energy sources. To sum up, changes in the electricity industry must be made carefully with respect to reliability requirements.