The effects of bioethanol addition to gasoline on an combined heat and power with internal combustion engine (ICECHP) are investigated experimentally and theoretically. In the theoretical study, a multi-zone spark ignition (SI) engine model is developed. This model was initially developed for gasoline fueled SI engine. However, it was adapted for SI engines running on gasoline-bioethanol blend. Experimental applications have been carried out with the gasoline fuel and the model results have been validated. Using the theoretical model, effects of bioethanol addition to gasoline on output temperature, flow availability, and efficiency are investigated. The results have shown when the bioethanol blend increases, the maximum cylinder pressure and temperature increase and carbon monoxide volume percentage reduces. Also, as the bioethanol blend increases, the availability of the flue gas increases as well. It is shown that among the various blends of gasohol, E20 has the maximum availability for heat recovery. The results of the efficiency investigation have shown that the efficiency of CHP is higher than the efficiency of separate heat and power (SHP) production. In fact, if the bioethanol blend in gasohol increases, the efficiency of the CHP system increases as well. It has been shown that E20 has the largest efficiency of ICECHP using gasohol. (C) 2007 Elsevier Ltd. All rights reserved.