[DB 1506 (20); OAB 65; ICR Creation Online] Underground oil deposits are always under a great amount of pressure, due to the weight of the material overlying them. The pressure does not leak away from these deposits, because the surrounding rock is also buried under the same pressure, and thus it is not at all surprising that pressurized oil deposits are found. Some versions of this claim point to certain oil deposits that are found to be under greater pressure than would be expected from the weight of the overlying material. One paper reporting these observations (P.A. Dickey et al,Science, v.160, pp.609-615 (10 May 1968)) was written before it was fully realized how extremely impermeable some rocks (such as certain forms of shale) can be to water. It is now known that these over-pressurized deposits are completely surrounded and sealed by impermeable layers, due to underground faulting. The formation and retention of these over-pressurized deposits is no longer a mystery.