Recovering waste heat from low- and medium-temperature sources is crucial for improving energy efficiency and reducing emissions. The basic organic Rankine cycle (B-ORC) offers an effective solution for this purpose. This study evaluates the performance of six working fluids (R290, R1234yf, R1233zd(E), R600a, R1234ze(E), and Novec649) using Python and the CoolProp library to model thermal and exergy efficiencies, network output, and required heat input. Results show that R290 achieves the highest energy efficiency (19%) and exergy efficiency (46%) but demands substantial heat input. R600a demonstrates strong performance, while R1234yf, R1234ze(E), and R1233zd(E) balance efficiency with environmental benefits. Despite lower energy performance, Novec649 stands out for its negligible environmental impact. This analysis provides critical insights into the trade-offs between energy performance and environmental sustainability, offering practical guidance for fluid selection in organic Rankine cycle applications across various operating conditions.