In recent years the addition of a hydrocarbon solvent (usually in the range of C4 to C20) to Cyclic Steam Stimulation (CSS) or Steam Assisted Gravity Drainage (SAGD) operations in heavy oil (bitumen) reservoirs has become an attractive process. We extend the idea of solvent addition to steam to a Vertical well Steam Drive (VSD), and investigate the recovery mechanisms, impact on the ultimate recovery and oil steam ratio. The process is studied in core flooding experiments and a CT scanner was used to monitor the saturation distribution over time. These results are history matched using Shell's in-house numerical reservoir simulator MoReS. The simulations show that the dominant recovery mechanism is facilitated through the formation of a solvent bank. Accurate modeling and understanding of the recovery mechanism enables optimal design of the solvent co-injection process in a vertical well steam drive. This allows a comparison between a VSD and a CSS development using solvent addition to steam and selection of the best development option for a given reservoir.