3D seismic data has been instrumental in deepening our understanding of leakage phenomena from hydrocarbon reservoirs. Specifically, we have learned a great deal about the risk of leakage through seal bypass systems. These encompass faults/fractures, intrusions, pipes and other small-scale geological features that compromise seal integrity by allowing relatively easy pathways through the seals by hydrocarbons. This talk summarises the evidence obtained from 3D seismic for the occurrence of seal bypass systems from a range of basin settings, and their potential as risk components in subsurface geological storage is discussed.