Heavy oil resources are assuming greater importance because of the increasing energy needs of the world. Compared to conventional oil, heavy oil is much more viscous and hence it presents many technical challenges at all stages of oil recovery and processing. In this work, a simple correlation, is presented here for prediction of heavy crude and tar sand oils viscosity as a function of kerosene volume fraction and temperature. The heavy crude and tar sand oils viscosity is calculated for temperatures in the range of 5 to 90°C and kerosene volume fraction up to 0.45. The proposed method is superior owing to its accuracy and clear numerical background, wherein the relevant coefficients can be retuned quickly if more data becomes available in the future. Estimations are found to be in excellent agreement with the reliable data in the literature with average absolute deviation being around 2%.