Both gravity-based solvent and cyclic solvent processes for recovery of heavy oil or bitumen may involve relatively high solvent/oil ratios. It has been experimentally observed that at high solvent loadings, the oil/solvent mixture partitions into a solvent-rich oil phase and a heavy-ends-rich oil phase. The partitioning may have significant beneficial impact on the performance of a solvent-based process such as VAPEX, or other gravity based processes if the low-viscosity phase carries the bulk of the oil production, and the asphalt-rich phase is mostly asphaltene and essentially immobile. Data on the physical properties (viscosity and density) and the composition of both the partitioned phases are needed to design and optimize solvent-based processes. The project objective was to analyze the laboratory test data on multiple phases partitioning of a selected oil/solvent system. The experiments, conducted with propane and Athabasca UTF bitumen at different solvent loading, have shown the oil/solvent mixture partitions into a solvent-rich oil phase and a heavy-ends-rich (mostly asphaltenes) oil phase with significantly higher densities and viscosities. CMG-WinProp software was used to model the phase partitioning. It was possible to get a good match between the test data on the liquid phase separations and some properties such as densities, but not viscosities.