Steam based thermal processes are major technologies for bitumen and heavy oil recovery. They are energy intensive, high water demand and huge CO2 emission. When such technologies are applied to the reservoir with thief zones, the economics are even worse. In order to increase the efficiency, people are trying to add solvent into steam to reduce the operation pressure and temperature so the economics. The mechanism of adding solvent into is further reducing the viscosity of bitumen or heavy oil an addition to thermal effects. That means the solvent should be dissolved into oil as soon as they meet each other at the interface. The boiling point of the solvent should be near that of steam. When it is to far from steam, it stays either liquid being produced without reacting with oil or gas stopping the heat exchange of steam. In this paper, PVT of some pure and commercial solvents is reviewed and potential operation pressure and temperature are discussed. This can help engineers to select solvent and design the process properly.