The study on caprock leakage in the North Sea consists of two aspects: first, leakage as Indicated by thermogenic wet gas, which was a survey study comprising the UK and Norwegian North Sea on fifty wells in forty fields. The second, a case study on Valhail well 2/8-8, which dealt with the geochemical evaluation of the caprock for leaked petroleum and the petrophysical characterization of the caprock. The result of the survey study indicate that thermogenic wet gas can serve as a reliable and diagnostic indicator of caprock leakage. High wet gas heights (i.e. ̲> lOOOm) were observed for fractured caprocks of high pore pressured reservoirs.