The Eastern Officer Basin in South Australia consists of a deep, east-west trending trough that flanks the southern margin of the Musgrave Block. From its northern margin south, to its axis the basin deepens with a very steep gradient, then shallows steadily to its southern margin. Superimposed on this regional configuration is a number of anticlinal structures. The deepest part of the basin, indicated by geophysical exploration occurs in the west and contains about 18,000 feet of basin fill. Drilling has penetrated 9,510 feet of these deposits which are no older than Silurian to Devonian. A Palaeozoic succession overlying Proterozoic sediments with marked angular unconformity is exposed along the eastern margin of the basin. The Palaeozoic, succession consists of 2,000 feet of doubtful Cambrian sediments, 6,000 feet of Ordovician and Devonian sediments and an unknown thickness of a molasse-type sandstone, of possible Carboniferous age. The presence of good porosity, in the Ordovician outcrops, the probability of shaley caprock in the distal areas of the basin and the occurrence of anticlinal structures demonstrated by geophysical exploration are encouraging features for petroleum exploration in this area.