In the present paper the performance of a waste heat recovery power generation system based on second law analysis is investigated for various operating conditions. The temperature profiles across the heat recovery steam generator (HRSG), network output, second law efficiency and entropy generation number are simulated for various operating conditions. The variation in specific heat with exhaust gas composition and temperature are accounted in the analysis and results. The effect of pinch point on the performance of HRSG and on entropy generation rate and second law efficiency are also investigated. The second law efficiency of the HRSG and power generation system decreases with increasing pinch point. The first and second law efficiency of the power generation system varies with exhaust gas composition and with oxygen content in the gas. Approximating the exhaust gas as air, and the air standard analysis leads to either underestimation or overestimation of power plant performance on both first law and second law point of view. Actual gas composition and specific heat should be used to accurately predict the second law performance. The present results contribute further information on the role of gas composition, specific heat and pinch point influence on the performance of a waste heat recovery based power generation system based on first and second law of thermodynamics. (c) 2006 Elsevier Ltd. All rights reserved.