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A state-of-the-art, characteristic-based upwind, interface capturing multiphase gas-liquid numerical formulation has been utilized to shed insight into the complex physics that characterize premature fuel nozzle shut-off during a typical refueling event. Interactions amongst several sub-processes are entailed which occur over widely different length and time scales. Detailed numerical simulations indicated that the physics is governed by: a) transient flow in vent and fill pipe during fuel nozzle shut-off; b) multiphase interactions at fuel/air/vapor interfaces and entrained air bubbles in fuel; c) formation of boundary layers in vent pipe and boundary layer displacement effects on wave propagation; d) formation of “vena contracta” at entrance to vent pipe; and, e) strong dependence of acoustic speed upon level of dissolved gases.