Abstract: A process is described for in situ recovery of bitumen or heavy oil from a reservoir having a horizontal injection well and a horizontal production well. The process includes a first phase in which steam and a heavy hydrocarbon solvent are injected into the reservoir, a second phase in which the steam and heavy hydrocarbon injections are transitioned to a light hydrocarbon solvent injection, and a third phase in which a light hydrocarbon solvent is injected without further steam or heavy hydrocarbon injection. A displacement gas may be added during any of the phases, and production of hydrocarbons continues throughout all phases. The process employs a high-production start-up phase, followed by lower cost phases which progress a depletion chamber within the reservoir.