The purpose of this paper has been to carry out an exergetic analysis of an innovative natural gas (NG) combined cycle cogeneration system (150-kW(e), 192-kW). The combined cycle is composed of a reciprocating Internal Combustion Engine (ICE), which is used as the topping cycle, and a water Rankine cycle (RC), which operates on the exhaust gases from the ICE, as the bottoming cycle. A steady-state model has been developed in order to identify and to quantify the exergetic irreversibilities of each component of the system and of the whole plant. Furthermore, a part-load exergy analysis, which shows the exergy performance in the operating field of the plant, has been carried out; finally, a sensitivity analysis pertaining to some performance parameters is presented. (C) 2010 Elsevier Ltd. All rights reserved.