The aim of this study is to investigate the economic optimization for an ORC system utilizing the geothermal energy. An economic parameter of net power output index, which is the ratio of net power output to the total cost, is proposed to optimize the ORC system using zero ODP and lower GWP working fluids. The maximum net power output index is obtained and the corresponding optimal pinch point temperature differences of heat exchangers are also evaluated for the ORC system. Furthermore, the analyses of the corresponding operating temperatures and pressures on the optimal economic performances of the CRC system are carried out. The effects of turbine inlet temperatures and their corresponding optimization are also discussed. The results show that R600 performs the most satisfactorily followed by R600a, R1233zd, R1234yf, R1234ze, and R290 under economic performance optimization. Moreover, the pinch point temperature differences in the evaporator vary more significantly than those in the condenser in optimal economic evaluations. The ORC system operated with R600, R600a, and R1233zd would have reductions in the proportion of equipment purchased cost from large to small attributed to lower operating pressures. (c) 2015 Elsevier Ltd. All rights reserved.