A new correlating parameter (CAPI) for heavy crude oils was developed. In this parameter, the API (American Petroleum Institute) oil gravity was corrected using a factor comprising compositional fractions (saturates, aromatics, resins, and asphltenes contents of the heavy crude oil). It was found that relating viscosity to CAPI was more representative than relating the viscosity to the API measurement alone. Using this new correlating parameter for the heavy crude oils considered in this study, two very different tendencies, defining a limiting value of 15, were observed. The viscosities of oils found under the limiting value of 15 were very sensitive to small changes in CAPI. An Omani heavy crude oil that showed higher viscosities compared to other crudes of similar API was found to be normal in terms of viscosity behavior when CAPI was used. In addition, crude oil viscosity could be predicted with more accuracy using this correlating parameter at different temperatures.