Abstract: Various embodiments include a method for determining a viscosity for heavy oil in a formation by obtaining viscosity data and nuclear magnetic resonance (NMR) relaxation time distribution data for a plurality of oil samples. A correlation is determined between a set of viscosity data for the plurality of oil samples and an NMR relaxation time geometric mean for the plurality of oil samples. An NMR relaxation time geometric mean intrinsic value is determined based on the correlation, apparent hydrogen index, and TE. Electromagnetic energy may then be transmitted into a formation and NMR relaxation time distributions determined for oil in the formation based on secondary electromagnetic field responses associated with the electromagnetic energy. A viscosity of the oil in the formation may then be determined based a correlation between the set of viscosity data and the NMR relaxation time geometric mean intrinsic value of the distribution data.