Four horizons were mapped (top of basement, top of Permian, top of Cretaceous and Sea Floor). The Denman Basin is a 50 km wide, north-south trending depression in Early Palaeozoic - Precambrian bedrock, infilled with up to 400 metres of Permian sediments. The fault-initiated depression appears to extend some distance to the north onshore beneath the Eucla Basin, but its southern offshore extent is more speculative. Overlying Cretaceous and Tertiary sediments of the Eucla Basin are areally much more extensive. These sands, clays and limestones were deposited in a stable platform regime whilst rifting and continental separation were taking place in the Southern Rift System. Extensive offshore Early Cretaceous channelling of the Permian sediments indicates that ancient zones of weakness associated with the Denman Basin provided a major conduit for Cretaceous sedimentation into the developing rift depocentres to the south. The Cretaceous sediments lying offshore gradually thicken from 150 metres thickness nearshore toward the south, and are up to 900 metres thick in the deepest palaeochannels. The hydrocarbon source potential of both basins is low due to shallow sediment burial depths, low total organic carbon contents and an uneventful low heat flow history. Potential external hydrocarbon sources include lateral migration from Mesozoic sources to the south and vertical migration from Early Palaeozoic - Late Proterozoic sources. Good reservoir and seal units are present although trapping mechanisms are subtle.