A new experimental apparatus was used to accurately measure the density and viscosity of aromatic solvents (toluene and xylenes), of Athabasca bitumen, and of their mixtures at different compositions. The measurements were taken under conditions applicable for both in situ recovery methods and pipeline transportation of heavy oil, that means, at temperatures varying from ambient temperature up to 343.15 K and at pressures up to 10 MPa and on mixtures with different weight fractions of the solvents (0.05, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6). The experimental density and viscosity data for the solvents and for raw bitumen were correlated using different correlation equations from the literature. Based on the experimental results, the influence of pressure, temperature, and solvent weight fraction on the density and viscosity of the mixtures was considered. The experimental density and viscosity data for the mixtures of Athabasca bitumen with toluene and xylenes were evaluated with predictive schemes as well as with correlation models representing certain mixing rules proposed in the literature. The density data are well predicted using an equation without adjustable parameter in which it is assumed that no volume change occurs. In contrast, the viscosity data are correlated reasonably over the studied conditions with Lederer's and power law models which include one adjustable parameter each.