The Birdsville Track Ridge (BTR) Block is dominated by a large, low relief Cambro-Ordovician basement' ridge which trends NNE-SSW through the block. Permian sediments onlap the eastern flank of the ridge, but only extend into the easternmost part of the block. Although existing as a major structural element, the BTR is not strongly fault-controlled, and the Mesozoic sequence thins gradually across the feature. Approximately 5000-7000 feet of Mesozoic section is preserved along the ridge, with the main horizon of thinning being the Triassic. Maturation profiles from drill cuttings indicate that locally the Jurassic sediments are of marginal to full maturity for oil generation, but significant migration may also have occurred from basin depocentres to the east. Exploration activity to date in the Block comprises 3 dry wells (2 drilled in 1963 and 1 in 1971) and 2388 line km of seismic (as part of 16 surveys shot until 1982), acquired within an area of 28,491 km2. Seismic mapping currently delineates 2 prospects, 10 strong leads and 9 weak leads, and for these the Block operator here reports a total estimated hydrocarbon potential of 27 MMSTB of oil plus 1 BCF of gas, assuming a 1 in 20 drilling success factor. Permian hydrocarbon potential in the Block is thought to be mainly confined to pinchout traps, plus perhaps some small independent structural closures. Triassic sediments present a moderate secondary target, in view of good oil and gas shows occurring to the west in the Pedirka Block. There they are generally fine-grained and tight, but with some cleaner sands which may prove more prevalent closer to the likely provenance on the BTR. The relatively undeformed Cretaceous-Jurassic sequence containing moderately thick fluvial sandstone reservoirs (i.e. Namur and Hutton formations) is the primary objective for oil. The Birkhead Formation, expected to be relatively sandy and therefore possessing poorer source rock and sealing properties than elsewhere where it has been drilled, has a downgraded potential. The Murta Member here also is thought to be very thin and unprospective, but the sandy overlying Cadna-owie Formation may thereby gain some reservoir potential. Most of the marine Cretaceous section is too shallowly buried and lacking in reservoir development to be considered prospective in this region.