The main recovery mechanism in the solvent-based bitumen recovery processes is gravity drainage. The density of heated bitumen or diluted bitumen at operational conditions is required to predict the production rate and cumulative oil recovery. In this manuscript, the densities of bitumen, pentane, and their mixtures at different pentane weight fractions (0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) have accurately been measured. The measurements were conducted under conditions applicable for both in situ recovery methods and pipeline transportation of heavy oil. The experiments were taken using Athabasca bitumen at temperatures varying from ambient up to 200 degrees C and at pressures up to 10 MPa. The volume change upon mixing for the mixtures is evaluated from the experimental results, and the influence of pressure, temperature, and solvent weight fraction on the volume change upon mixing and density is studied. The density data are also represented with three different approaches considering no volume change, excess volume, effective liquid densities, and equation of state. The results indicated that the mixture data are well-predicted using equation of state and effective liquid densities with average absolute relative deviations (AARD) of 0.55% and 0.57%, respectively.