Abstract Unconventional oils are very viscous and immobile at reservoir conditions; hence, recovery techniques that are used in conventional reserves are not applicable and practical for heavy oil and bitumen resources. Thus, addition of heat or solvent is required to reduce viscosity of these fluids for both recovery from reservoir and transportation. Thus, in this study, the viscosity of Athabasca bitumen and n-hexane mixtures was measured at different temperatures, pressures, and solvent weight fractions. The results indicated a huge reduction in viscosity of bitumen by increasing the temperature and/or dissolving the solvent. The viscosity of the mixtures showed a curvilinear trend with respect to the solvent weight fraction and temperature. The impact of pressure on the mixture viscosity is more pronounced at lower solvent weight fractions and lower temperatures. The evaluation of different models for mixture viscosity indicated that the power law and Cragoe׳s models represent the viscosity data over wide range of operating conditions better than other models.