Jurassic and Triassic reservoirs in the Central North Sea are characterised by deep burial (>4000m) and high overpressures (>40 MPa above hydrostatic). These reservoirs form the high-pressure/ high-temperature (HPHT) play. Overpressure forms a problem for safe exploitation of these reservoirs; it can also provide a clue to the hydrogeological environment of the region, and thus provides insight into hydrocarbon migration, entrapment and diagenesis.