A regional stratigraphic analysis, using mainly quantitative data derived from wireline logs, has led to the reconstruction of the palaeogeography and depositional history of the Permian Gidgealpa Group within the southern Cooper Basin. The Cooper Basin is an infrabasin containing up to a 1600 m thickness of Gidgealpa Group sediments, which covers an area of 60 000 square km near the centre of Australia. It contains major reserves of natural gas and minor amounts of crude oil trapped in fluvial to marginal marine sandstone reservoirs within coal measures. Lithofacies analysis of a sequential set of palynologically defined time-rock units spread through the Gidgealpa Group has clarified depositional trends, identified regions of optimum channel locations, located positions of shorelines, and shown directions of marine transgressions and regressions. Detailed core study, investigation of the cyclic nature of sedimentation, and linear regression analysis have helped to elucidate depositional environments. Gidgealpa Group deposits were laid down from rivers, lakes, coal swamps and large inland 'seas', during a period when the geomorphic relief diminished with time. As a result, the earliest fluvial deposition was from braided streams, whereas subsequent periods experienced mainly meandering rivers in a floodplain environment. Braided streams deposited the Tirrawarra Sandstone on a possibly glacially scoured land surface. As topographic gradients declined, rivers began to meander, and sandstones, shales and coal deposits of the Patchawarra Formation encroached over Tirrawarra Sandstone. Northwards flowing rivers entered the basin at its southern extremity, where valleys were gradually filled by sediment. Few major rivers reached the northern part of the basin, which received mainly overbank deposits. During uppermost Patchawarra Formation deposition, the Cooper Basin was invaded from the east by an inland 'sea', which deposited the Murteree Shale. As this 'sea' retreated, shoreline sediments of the Epsilon Formation built out towards the east. During a second transgressive pulse the land was once more inundated, and the Roseneath Shale was deposited. Finally, deltas of the Daralingie Beds prograded eastwards, in the wake of the retreating sea. A long period of uplift and erosion followed, during which time the present structural grain was imposed on the basin. By the time deposition commenced once more, the land surface was flat except for a few hills rising above the plain, and meandering rivers entered the basin from the west, depositing sandstones, shales and coal of the Toolachee Formation as they flowed eastwards. Accumulation of the Gidgealpa Group ended when the climate, perhaps, became unsuitable for continued deposition of the Toolachee Formation coal measures. On a continental scale, Cooper Basin palaeogeography is related to that of the Permian basins to the east, all of which ultimately had access to the open sea somewhere in the vicinity of the present day coastline. The Cooper Basin holds considerable scope for future petroleum discoveries in anticlines and fault traps. In addition, stratigraphic traps hold great potential, especially valley traps resulting from onlap, as well as shoreline and channel sandstones enclosed in shales.