Pore-fluid pressure gradients in Lower Tertiary to Upper Jurassic mudrocks in the Gullfaks area show significant variations, both between and within individual structural compartments. Detection and quantification of abnormal pore-pressures, based on drilling parameters and wire line logs, are significantly influenced by petrological variations in the mudrocks and do not provide adequate direct pressure indicators. Empirical models show that the degree of overpressuring in mudrocks above the Gullfaks reservoirs cannot be fully explained by processes such as shale dehydration, compaction disequilibrium, aquathermal effects or in situ hydrocarbon generation, and other processes, such as caprock failure and subsequent migration of hydrocarbons (mainly gas) into the overlying mudrocks, appear to be influential in generating the observed pattern of overpressure.