Cogeneration cycles have many advantages over the conventional cycles. In this study, the performances of the simple and the air preheated cogeneration cycles are compared with each other. To calculate the enthalpy and entropy values of the streams, a computer program written by the author in FORTRAN codes is used. Exergy analysis is done for the simple and the air preheated cogeneration cycles. The results present that by changing the compression rate from 6 to 16, the electric power increases about 20 %, but the heat power decreases about 11 % for the simple cycle. By changing excess air rate from 1.3 to 3.5, the decrease of the heat power and the heat exergy power are about 20 % for the simple cycle at compression rate 6. Increasing compression ratio increases the exergetic efficiency for the two cycles. Maximum efficiencies are obtained about 2 and 2.5 excess air rates for the simple cycle. For the air preheated cycle increasing excess air rates increases the exergetic efficiency.