Three kinds of energy service system were examined as alternative energy systems in urban areas. A comparison of these energy systems was performed by finding Pareto optimum solutions for a multi-objective model. The model had two objective functions: CO2 emission and cost to consumer. Various energy pricings were provided in the model as variables. The assumed alternative systems were those in which: (1) every consumer had a cogeneration system (CGS); (2) there was a centralized energy supply plant (ESP) that had a CGS installed and supplied energy (electricity, gas, cooling and heating) to consumers; and (3) both (1) and (2) were installed. Minimization of CO2 emissions and minimization of cost to consumers were assumed as objective functions of the multi-objective model. Energy prices that consumers paid were used in the model as variables. We performed an analysis and comparison of the three kinds of system from the viewpoints of CO2 emission, economic impact on consumers and ESP, using system operations as evaluation indexes. (c) 2005 Elsevier Ltd. All rights reserved.