Abstract: Described is a method of operating a cyclic solvent-dominated recovery process (CSDRP) for recovering viscous oil from a subterranean reservoir of the viscous oil to enhance recovery effectiveness. The cyclic solvent process involves using an injection well to inject a viscosity-reducing solvent into a subterranean viscous oil reservoir. Reduced viscosity oil is produced to the surface using the same well used to inject solvent. The process of alternately injecting solvent and producing a solvent/viscous oil blend through the same wellbore continues in a series of cycles until additional cycles are no longer economical. Conventionally, the solvent composition remains constant over time within each injection cycle and among cycles. In the present method, by contrast, the solvent composition is varied over time thereby providing operational benefits as described herein.