The effects of blade discharge angle on the performance of a standard industrial centrifugal oil pump of type 65Y60 were investigated experimentally as the pump handled both water and viscous oil. A one-dimensional hydraulic loss model was established to identify such effects mathematically. The effects have been estimated analytically by using the model at various viscosities. The results showed that the blade discharge angle has significant but equal influence on the head, shaft power and efficiency of the centrifugal oil pump at various viscosity conditions. For any viscosity, the total hydraulic loss in the impeller and volute rises with increasing blade exit angle. The diffusion loss in and behind the impellers as well as the friction loss in the volute are noticed in the pump, especially for highly viscous liquids. The hydraulic loss in the impellers is about 0.8-0.6 times the loss in the volute. In order to improve the pump performance, the hydraulic loss in the volute must be kept as small as possible.