Predictions for viscosity of Saskatchewan heavy oils are validated with experimental data at various temperatures and a wide range of pressures. Comparisons of predictions made with a single measured value and curve-fit value both at 30-degrees-C and 0 MPag pressure showed that results obtained with the later were in better agreement with experimental values; with overall average absolute deviations of 6.9% and 2.9%, respectively. The results demonstrated that extreme care is essential in measuring viscosity at the reference temperature if accurate prediction is to be achieved with the correlation; and furthermore that the correlation can successfully predict heavy oils viscosity.