In this paper, a subcritical and supercritical organic Rankine cycle (ORC) are designed to recover exhaust gas waste heat of biogas fuelled combined heat and power (CHP) engine. The CHP engine is located in Belgium and uses biogas as fuel which is produced from the digestion of domestic wastes by anaerobic digestion. R245fa is selected as working fluid. First, the system parameters as net power, mass flow rate, pumps total power consumption, total evaporator exergy inlet, thermal efficiency and exergy efficiency are improved by changing turbine inlet temperature and pressure. After which second low analysis of the overall system and system components are determined for the best performed subcritical and supercritical cycles. Compared with subcritical ORC, the supercritical ORC has shown better performance. The best performed cycle net power, thermal efficiency and exergy efficiency are evaluated as 79.23 KW, 15.51% and 27.20% for subcritical ORC and 81.52 kW, 15.93% and 27.76% for supercritical ORC, respectively. (C) 2016 Elsevier Ltd. All rights reserved.