Interpretation of 2D seismic reflection data combined with correlation of five wells in the southern part of the Central Irish Sea Basin show a NE-SW trending graben, whose bounding faults are considered to be reactivated lineaments of Precambrian age. The basin-fill comprises mainly Carboniferous and Triassic successions, with localised and thin occurrences of lower Jurassic and Tertiary rocks, all of which are unconformably overlain by Quaternary sediments. Due to poor data quality, the structural evolution of the area during the Late Palaeozoic is poorly understood. During the Triassic, the basin was subjected to thermal subsidence with a phase of minor uplift in the Anisian. The major phase of extension in the basin took place during the ?Middle - Late Jurassic and had a NW-SE orientation. Subsequent Late Jurassic sinistral shear along the NE-SW trending basin bounding fault is suggested to have taken place, giving rise to a series of north-south intra-basinal faults. The present-day structure of the basin is a broad anticline, inherited from a Cretaceous - Early Tertiary compressional phase. During the Palaeocene the area was subjected to regional uplift, followed by minor extension along the NW boundary fault during the Eocene - Oligocene. A Late Tertiary phase of transpression is postulated to have occurred, which inverted north-south trending faults and folded the base-Tertiary unconformity.