Interpretation of seismic lines from the offshore NE Wales area has provided information on the structural and stratigraphic evolution of the southern part of Morecambe/Liverpool Bay. Basin-wide megasequence boundaries are present between the Dinantian and overlying sequences and between the Upper Carboniferous and Permo-Triassic megasequences. Geological information obtained from seismic lines has been used to construct an E–W geological cross section and a basin analysis summary chart for the NE Wales–Cheshire onshore area. Stratigraphic interpretations have been considered in an assessment of the petroleum potential of the region. The distribution of Carboniferous oil and gas prone source rocks is a key element in predicting hydrocarbon accumulations. Source rock maturity may have been reached in the offshore area prior to a phase of inversion and uplift during Tertiary times. Fault-controlled hydrocarbon traps generated during Triassic-Jurassic rifting were modified during Tertiary inversion and new structures were generated.