Solution-gas drive in heavy oil reservoirs is a complex! process, and the mechanisms involved are not fully understood In the past, these reservoirs have been modelled by altering variables such as critical gas saturation, bubble point pressure, relative permeability curves, fluid properties, and rock properties during sand production. Numerous investigations have shown that gas mobility in heavy oil remains extremely low. Furthermore, experimental observations have suggested that gas mobility depends not only on gas saturation, but also on depletion rate and oil viscosity. It is therefore thought that the viscous forces at the microscopic level affect gas mobility. The dependence of relative permeability to gas on parameters other than gas saturation has been I, observed previously in processes such as foam flow through I porous media, and displacement near miscible conditions, where 1 the ratio of viscous forces to capillary forces is large. In this work, we have developed a numerical simulator where the "apparent" gas relative permeability is a function of rate and! gas saturation. The developed model is used to simulate a previously reported set of experiments of solution-gas drive in heavy oils, where the dependence of gas mobility on depletion rate has been observed. It is shown that a model with rate-dependent relative permeability functions can explain many features of solution-gas drive in heavy oil, in particular, its rate-dependent recovery behaviour.