This article presents experimental results on the mixing of CuO nanoparticles in ISO VG 46 oil, Jatropha oil, and a blend of the two oils. Initially, blend oil was prepared by mixing ISO VG46 and Jatropha oil in a fixed proportion. This blending caused a reduction in the viscosity of the oil mix as compared to the ISO VG46 oil. Therefore, to bring the viscosity of the blend oil to the level of the ISO VG46 oil, various concentrations of CuO nanoparticles were added to the blend to prepare stable nano-blend oils. The stability of the blend oil, ISO VG46, and Jatropha oil-based nano-lubricants was checked by measuring viscosity at regular intervals of time, and it is observed that stability decreases with the increase of CuO loading in base fluid. Viscosity values of nano-blend oils for various concentrations of CuO ranging from 0 to 3 wt. % were measured. These values were compared to the viscosity values of ISO VG46 and Jatropha oil-based nano-lubricants with the same CuO concentrations. About 19, 17, and 20 % enhancement in viscosity was observed in the blend oil, ISO VG46 oil, and Jatropha oil-based nano-lubricants, respectively, for 3 wt. % concentrations of CuO at 30°C. The nano-blend oil showed inferior performance up to 2 wt. % concentration of CuO in the entire temperature range (30 to 60°C). The viscosity of the nano-blend oil dispersing with 3 wt. % concentration matched well with the viscosity of ISO VG46 mineral oil. Furthermore, the experimental viscosity data of all the types of nano-lubricants are compared to the different viscosity models, and it is observed that the viscosity of the nano-lubricants closely matched with a viscosity model available in the literature. It is observed from viscosity sensitivity analysis that viscosity is more sensitive to greater concentration. The studies on the effects of nanoparticles’ concentration on density and friction coefficients revealed that the addition of nanoparticles in base oils had a small impact on pumping power.