The Officer Basin is an elongate intracratonic depression underlying western South Australia and eastern Western Australia, and bounded by the Musgrave, Gawler and Yilgarn Blocks. Its southern and eastern margins are overlapped by the Tertiary Eucla and Permian Arckaringa Basins respectively. In its broadest definition, it contains a sequence of Late Proterozoic to pre-Permian sediments with an unknown number of stratigraphic breaks. Previous basin study work carried out in South Australia included the drilling of two unsuccessful wildcat petroleum wells, the drilling of two other stratigraphic wells, and limited acquisition of seismic and gravity data. Recently completed investigations by the South Australian Department of Mines and Energy, centred along the eastern margin of the Officer Basin, have upgraded the petroleum potential of the basin in South Australia. In 1976 SADME Murnaroo 1 intersected shales and carbonates, with moderate organic carbon contents, overlying a thick, porous sandstone. SADME Wilkinson 1, drilled in 1978, was a regional stepout from Murnaroo 1 that intersected a carbonate-evaporite sequence and terminated in low-porosity sands. The carbonates showed excellent potential for oil generation, containing marginally mature oil-prone source rocks. Acritarchs extracted from these carbonates indicate an Early Cambrian age. In 1979 SADME Byilkaoora 1, drilled in the north-eastern Officer Basin, discovered the basin's first oil shows bleeding from partly sealed vugs and fractures in argillaceous carbonates. This sequence also contains abundant non-marine evaporite pseudomorphs, with chert nodules and cherty interbeds. SADME Marla 1A and Marla 1B, drilled near Byilkaoora 1, both penetrated equivalent carbonates beneath the north-western margin of the Arckaringa Basin. Recent ground mapping in the eastern Officer Basin, and a helicopter-based geological survey in far western South Australia, have complemented this drilling to increase the knowledge of the character and distribution of Palaeozoic rocks within the basin. All ?Cambrian carbonate sequences recognised to date in the Officer Basin of South Australia are correlated with the Observatory Hill Beds, which are now established as the major potential generator of petroleum in the eastern Officer Basin.