Viscous petroleum may be recovered from viscous petroleum-containing formations including tar sand deposits by contacting the formation with a heated multiple-component solvent for the petroleum. At least one solvent component is normally gaseous material such as methane, ethane, propane or butane and at least one component is normally liquid, such as pentane and higher molecular weight hydrocarbons. The solvent mixture is heated to a temperature in excess of ambient temperature, and preferably from 100.degree. to 500.degree. F. prior to injection into the formation. The multiple solvent is introduced under sufficient pressure that it is substantially all liquid at the injection conditions. Recovery of petroleum and solvent may be from the same well as is used for injection or from a remotely located well. When the pressure in a portion of the formation contacted by the solvents is reduced below the bubble point pressure of the solvent-bitumen solution, the solvents vaporize to provide a solution gas oil recovery mechanism. The normally liquid components dissolve in the petroleum and reduce the petroleum viscosity.