One of the important mechanisms in solvent-aided thermal recovery processes is viscosity reduction due to dissolution of solvent in the bitumen. This dissolution occurs either with the condensed solvent at the edge of the steam chamber or with direct contact of gaseous solvent and bitumen. Therefore, it is essential to determine the solubility and viscosity of solvent in bitumen for reservoir simulation of solvent-aided thermal recovery processes. We report new experimental viscosity and solubility data of methane-, ethane-, propane-, and butane-Athabasca bitumen systems at high temperatures (up to 260 degrees C). The experimental measurements have been conducted under liquid-vapor equilibrium conditions. Peng-Robinson Equation of State (PR-EoS) was employed to model the solubility data. The tuned PR-EoS represented the experimental solubility data of methane, ethane, propane, and n-butane in bitumen with absolute average relative deviations of 5.7, 4.1, 7.8, and 4.9%, respectively. The reported data find applications in reservoir simulation studies of the solvent-aided thermal recovery processes.