Project Final Report-08121-2201-02-The objectives of this work are to evaluate current practices in viscosity measurements, correlations, and models of heavy, viscous oil, to include experimental validation of the models; develop best practices of sample handing and laboratory measurement methods; study the impact of solvent and commingling of different fluids on viscosity change and asphaltenes instability, including examination of the existing models and mixing rules in handling the property change; and report on conditions in which multiple phases exist.