During a solvent-based heavy oil recovery process, asphaltene precipitation may occur when a solvent is dissolved into heavy oil under certain reservoir conditions. Thus, such an in-situ upgraded heavy oil with a lower asphaltene content is less viscous and easier to be recovered. In this paper, enhanced solvent dissolution into the in-situ upgraded heavy oil is studied. First, three heavy oil samples with different asphaltene contents are tested to model the upgraded heavy oils to rather different extents. Then the propane solubilities in these three heavy oil samples and the viscosities of the three heavy oil-propane systems are measured at five equilibrium pressures ranging from 200 to 800 kPa. Also, the propane diffusivities and oil-swelling factors of the three heavy oil-propane systems are measured by applying the newly developed dynamic pendant drop volume analysis (DPDVA) method in the same pressure range. The detailed experimental results show that the asphaltene content in heavy oil strongly affects propane dissolution into the heavy oil. The propane solubility in the maltenes is found to be the highest, which results in the largest oil-swelling factor among the three heavy oil samples tested. Expectedly, the viscosity of the heavy oil-maltene system is the lowest and accordingly the propane molecular diffusivity in the maltenes is the largest. The in-situ upgrading of heavy oil during a solvent-based recovery process greatly enhances further solvent dissolution into heavy oil and reduces its viscosity. (c) 2007 Elsevier B.V. All rights reserved.