VAPEX (vapour extraction) is a non-thermal process that has significant potential to provide a more environmentally friendly and energy-efficient alternative to steam injection. While numerical modelling techniques are available for simulating mass transfer in VAPEX process, computational constraints often preclude detailed numerical solution of the flow and transport differential equations, as is often implemented in traditional flow simulators. Efficient alternatives that are based on analytical solutions could be employed to assess the transport physics. In this paper, a novel physical-based proxy is developed to model solvent transport in VAPEX at isothermal conditions, in a way analogous to the SAGD model described by Butler (Butler, J. Can. Petrol. Technol. 1985, 24, 42). Detailed analytical formulations are derived and implemented in a calculation procedure to advance the solvent-bitumen interface and to estimate producing oil rate with time. In our approach, solvent concentration and intrinsic diffusion coefficient are introduced in the model instead of temperature and thermal diffusivity in SAGD. A new mass penetration parameter is introduced and its change with time is modelled. Growth of solvent chamber and oil drainage rate predicted from the proxy model are in good agreement with Hele-Shaw experimental data available in the literature. Results predicted by proxy model also match well with scaled-up flow rates for a field case described by Das and Butler (Das and Butler, J. Can. Petrol. Technol. 1994, 33, 39).