A generalized viscosity model suitable for describing the non-Newtonian behaviour of waxy crudes has been developed. The model, which has the following expression predicts the viscosity as a function of shear rate, temperature, and wax concentration : mu = B-1/gamma [(gamma+A(1)/A(1))(n)-1]((1/n))e((C/T+DxW)) where mu is the viscosity, gamma is the shear rate, T is the temperature, and W is the percentage of wax. The viscosity measurements were performed by measuring the rheological properties of the waxy oil at four different concentrations and five different temperatures. A reduced form of the model may be used to predict the viscosity of Newtonian and non-Newtonian fluids with or without yield stress. The proposed model was found to fit the experimental data well as demonstrated by a high coefficient of correlation (97.5%). The nonlinear regression analysis was used to determine the model parameters A, B, C, and n. (C) 1998 Elsevier Science S.A. All rights reserved.