The viscosity of heavy oils is a critical property in predicting oil recovery. Viscosity plays an important role in reservoir simulations as well as in predicting the easiness of fluid flow, selecting a production approach, and predicting oil recovery. In this work a simple-to-use predictive tool has been developed to predict the viscosity of heavy oil as a function of temperature as well as a simple correlating parameter that can be used for heavy oil characterization. The reported results are the product of analysis of many heavy oils data collected from the open literature for various heavy oil fields around the world. The tool developed in this study can be of immense practical value for petroleum engineers to have a quick check on the viscosity of heavy oil without opting for any experimental trials. In particular, petroleum and production engineers would find the proposed correlation to be user-friendly with transparent calculations involving no complex expressions.