Expulsion of geopressured fluids along and/or across fault zones has been proposed as an important transport process in sedimentary basins. A variety of phenomena, including hydrocarbon migration, pressure, temperature and salinity distribution, mud volcanoes, and active vent sites, could be influenced by this mechanism. I present results of numeric simulations for fluid flow along and across a schematic growth fault that has a strong pore-pressure-dependent permeability related to microfractures. The results from these simulations are compared with model simulations in which the fault is either impermeable or has a permeability based on the relative proportions of sand and clay within the deformation zone (clay smear model). If initial fluid pressure is high and thus effective stress is low, then a relatively long period (hundreds of years) of moderate fluid velocity fluid flow results. At first, only the lower part of the fault where fluid pressures are near lithostatic is hydrologically open. However, upward transport of fluid raises pore fluid pressures and opens the upper part of the fault. Significant cross-formational fluid flow occurs at this time, and in some instances, the flow direction in the sands adjacent to the fault zone reverses direction. Eventually, pore fluid pressure decreases, effective stress increases, and fracture permeability collapses starting from the bottom of the fault. All or part of the fault becomes a barrier to subsequent fluid flow. If initial regional fluid pressure is low and thus effective stress is high, then only the lower part of the fault is open, and upward fluid flow is insufficient to raise excess fluid pressures enough to open the entire fault. Cross-formational fluid flow is inhibited. Finally, I ran fluid-flow simulations with elevated fluid pressure within the fault zone itself. Generation of this additional fluid pressure is presumed to be caused by ductile shear or some other process during active fault movement but is not explicitly computed in the simulations. Elevated pore fluid pressure in the fault zone can produce short bursts (duration of years) of rapid, kilometer-scale vertical transport along fault zones. During these short expulsion events, fluid movement is mostly upward along the fault zone and then lateral into stratigraphically higher sands. After the short burst of fluid expulsion, these simulations follow a similar fluid-flow history to model simulations without elevated pore fluid pressure in the fault zone. All simulations show that fault zones must remain barriers to fluid flow during most of their history, or geopressures would dissipate within tens of thousands of years.