This study presents a thermal performance comparison of various working fluids operating in a parabolic trough collector. Fluids such as gases (helium, carbon dioxide, and air), liquid sodium, and liquids (pressurized water, Therminol VP1, and Syltherm 800) are evaluated. This study also examines the efficiency enhancement obtained from the dispersion of copper nanoparticles in water, Therminol VP1, and Syltherm 800 base fluids. The optimum parameters for nanoparticle concentration, volume flowrate, and inlet temperature to obtain the maximum efficiencies for each working fluid were evaluated in this study. The thermal model used in this study was modeled after the commercially available LS-2 collector, which is designed in the engineering equation solver (EES) and validated with results found in the literature. The results of the study show that the Cu/Syltherm 800 nanofluid showed the most enhancement in thermal efficiency with 0.141%, while Cu/water and Cu/Therminol VP1 had enhancements of 0.037% and 0.088% respectively.