Benchmarking the performance of local energy systems requires an integrated approach. This paper develops a composite index that consists of a unique set of 7 dimensions and 35 main indicators. The SDEWES (Sustainable Development of Energy, Water, and Environment Systems) Index is applied to a sample of 22 Mediterranean port cities. The index integrates energy and CO2 emissions data from SEAP (Sustainable Energy Action Plans). The values of the indicators are aggregated based on the Min-Max method for a final ranking. Nice, Venice, and Dubrovnik are the top three cities. An average city in the sample receives a composite score of 2.71. The results are subjugated to comparison based on three energy scenarios. The scenarios take into account reductions in final energy consumption per capita for a given area of the city based on smart energy measures. The scenarios represent improvements in the energy system that may include combined heat and power based district heating networks. A SDEWES Index Tool is developed to further allow cities to plan for potential changes in the final ranking based on energy scenarios. The SDEWES Index is useful to trigger learning, action, and collaboration among Mediterranean port cities to increase future performance. (C) 2015 Elsevier Ltd. All rights reserved.