Gas-oil relative permeability is essential for performance predictions of reservoirs with solutions for gas drive, gas cap expansion, or gas injection. The nature of flow in reservoir is determined by the interplay of relative permeability and viscous, gravity, and capillary forces. Displacement experiments of the gas-oil system are performed on long core scale models by varying the petrophysical properties and flow conditions. Experiments are conducted in situations where capillary, gravity, and viscous forces are comparable. The effect of destabilized front velocity on relative permeability and residual saturation is investigated. The results indicate that the relative permeability varies with the balance between the gravity and viscous forces. The relative permeabilities determined by analytical and numerical approaches indicate that higher displacement velocity leads to a higher gas relative permeability and lower oil relative permeability. The residual oil saturation was increased by increasing the injection velocity and decreasing the permeability.