This study compares the performance of a thermal power plant fired by natural gas to that fired by biodiesel blend, from exergetic and economic perspectives. A thermodynamic model has been developed to predict the performance of a running plant and was used to conduct the comparative study. Plant life of 25 years has been used to assess the viability of the gas turbine power plant by analyzing the net present cost and the break-even point for both fuels. The plant specific fuel consumption for natural gas fired and biodiesel blend fired are 0.3151 [kg/kWh] and 0.3884 [kg/kWh] respectively. The system fired by natural gas only, has a payback period of 1.9 years, internal rate of return of 52% and exhaust temperature of 915.74 [K], while that fired by the biodiesel blend has a payback period of 2.4 years, internal rate of return of 60% and exhaust temperature of 858.50 [K]. Nevertheless, biodiesel blend is preferable because it is biodegradable, produces less emissions, and as a consequence, environmentally benign. Biodiesel blend would be more suitable for firing gas turbine engines, if the combustor is redesigned to improve its efficiency. Fhermo-economic analysis of gas turbine power plants is essential to improve its thermodynamic and economic performance. (C) 2018 Elsevier Ltd. All rights reserved.