Increase in population and energy demands are causing more energy consumption in Turkey. As a parallel of increasing energy demands, Turkey's carbon emissions are on the rise, per capita energy consumption and per capita carbon emissions are trending upwards. Because of the economic and environmental reasons, cogeneration system is very important for Turkey. In addition to the energy and cost savings, the benefits of cogeneration system are mainly concentrated from lower air pollutants emissions to the atmospheric environment, in particular carbon dioxide and nitrous oxide. The main aim of this article is to identify and discuss some of the important and critical decision criteria to select the best cogeneration system providing the most satisfaction with the help of fuzzy AHP (analytic hierarchy process) and fuzzy TOPSIS (technique for order preference by similarity to ideal solution) methods for a prominent hotel in Istanbul. The decision process is analyzed with a real case application for one of the biggest hotel's needs in Istanbul. Also, Turkey wants to select the most appropriate cogeneration system to meet of hotel' s electricity and heat requirements. By the way, the results of fuzzy AHP are compared with the results of fuzzy TOPSIS. (C) 2013 Elsevier B.V. All rights reserved.