Abstract: There is disclosed a process of oil recovery from tar sands or separation of hydrocarbons from a solid or viscous bitumen source wherein carboxylic acids or carboxylic acid mixtures are utilized as a solvent or diluent and are mixed with heavy crude oil, injected into an oil reservoir or mixed with tar sands in a surface vessel to reduce the viscosity of the crude oil and to increase the mobility of the oil. The process is characterized by the use of an amphiphilic phase separation induced by injection of isopropanol or other alcohol to facilitate the recovery of carboxylic acid diluent from the bitumen product, and another phase separation step may be employed to separate the carboxylic acid component from the alcohol. Sodium chloride or other brine solution is usually mixed with the alcohol and many embodiments combine a light hydrocarbon such as heptane with the carboxylic acid as an additional solvent. Carboxylic acids in the form of fatty acids with from 8 to 20 carbon atoms are preferred.