The presence of a salt sheet in the subsurface provides a permeability barrier to the flow of fluids, which can lead to the development of an overpressure condition and slower rate of compaction for formations underlying the salt sheet. These effects are demonstrated through (a) numerical simulations and (b) observations from four wells in the Gulf of Mexico which penetrated salt sheets and tested the underlying formations. The numerical models simulate the time-dependent fluid flow in a sedimentary basin containing a salt sheet; these models predict a significant increase in excess pore pressure in subsalt formations relative to the regional...