There has been a great deal of uncertainty with regard to the existence and nature of pressure seals. Overall, researchers studying anomalous pressure fall into one of two categories: those who accept the existence of effective seals and those who do not. Researchers who do not believe seals exist support classic hydrologic interpretations that suggest anomalous pressures are bounded by low-hydraulic- conductivity rocks and are, therefore, geologically ephemeral. Those who do believe seals exist, for the most part, do not present specific evidence of what comprises a seal. Although the sealing capacity of various rocks for hydrocarbon accumulations has been investigated, very little research has been conducted specifically concerning the seals that contain anomalous pressures. The influence of capillary forces on hydrocarbon entrapment is widely recognized, but capillary phenomena have largely been ignored in studies dealing with geopressures, even though hydrocarbon generation is commonly cited as the mechanism by which overpressure is generated. The delineation of pressure compartments, especially those of known geologic duration, is an important tool by which potential seals can be mapped and investigated. Without specific knowledge of seal characteristics, well-founded interpretations of seal effectiveness and pressure compartment longevity cannot be made.