Viscosity is a key property for evaluation, simulation and development of petroleum reservoirs. The accurate prediction of viscosity will be helpful for, production forecasting, designing future of thermal recovery processes. Reservoir oil viscosity is usually measured isothermally at reservoir temperature. However, at temperature other than reservoir temperature these data are estimated by empirical correlations. Here, based on results of viscosity measurements of 33 heavy crude oil samples of API gravity ranging from 10° and 20° degree, at 68 °F collected from various areas of Kuwaiti oil fields, and tested at 68 to 320 °F. A new correlation has been developed. The validity and accuracy of this correlation has been confirmed by comparing the obtained results of this correlation with other ones along-with the experimental data. The result were satisfactory, in contrast to other correlations which were mostly developed for significantly lighter oils at average reservoir temperatures. Most of them cannot reasonably predict the heavy oil viscosity at elevated temperatures.