Liquid viscosities of reservoir crude oils of Fuyu and Huabei in China were measured at six temperatures and high pressures. The semitheoretical viscosity model developed by the authors for pure liquids was successfully extended to reservoir crude oil systems by applying simple empirical mixing rules. A Comparison of the viscosities predicted with the proposed model and those predicted with the commercial software package-STATPACK has been presented significant improvement was obtaived by LVIS.