Bitumen liberation is known to be an essential step for bitumen recovery from sand grains using the current warm/hot-water-based extraction process. This study aims at understanding the role of naphtha or toluene addition in enhancing bitumen liberation. Results from an in situ bitumen liberation visualization measurement indicate that soaking two oil sands ores by solvents at 10-30 wt % of the bitumen could significantly enhance not only the ultimate degree of bitumen liberation (UDBL) but also the rate of bitumen liberation (RBL) in the process water at ambient conditions. Although ore-type- and solvent-type-dependent, both the UDBL and RBL would increase sharply at 10-20 wt % solvent dosage. A further increase in solvent dosage showed a diminished increase in the UDBL. To understand the observed improvement, viscosities of bitumen directly extracted from the ores and its mixture with solvents were measured, as well as diluted bitumenwater interfacial tensions. Results showed that adding solvent into the bitumen reduced bitumenwater interfacial tension and more so for the reduction in bitumen viscosity. Interestingly, the viscosity and interfacial tension of diluted bitumen were found to be dependent upon the source of ores and type of solvents. The UDBL was found to be inversely correlated with the interfacial tension and bitumen viscosity, while the RBL correlated almost linearly with the interfacial tension/viscosity ratio, which acted as the balance of the interfacial tension driving force/adhesion drag force. These correlations were less dependent upon the types of ores and solvents.