The paper deals with an innovative (120 Me, 195 kWt) natural gas (NG) combined heat and power (CHP) system, at present under development, which has been set up at the FIAT Centre of Research (CRF), Turin, Italy. The main characteristics of the CHP system are: the use of an automotive derived internal combustion engine, a high part load electrical efficiency due to a variable speed operation strategy and an advanced exhaust gas after-treatment to meet the most stringent pollutant emission regulations. In the paper, the electrical efficiency and pollutant emissions of the new CHP unit are compared with those of some traditional small-scale cogeneration systems. Some comparison criteria and performance indices which are, in the authors' opinion, the most representative of the real operative conditions, have been proposed to evaluate the performance of the different technologies. (c) 2006 Elsevier Ltd. All rights reserved.