The Cooper Basin is an infra-basin (area 127 000 km2) containing a Permian to Triassic age succession which is overlain by Jurassic and Cretaceous age sedimentary rocks of the Eromanga Basin. Coal beds occur throughout the entire section. Oil and natural gas are known to exist in reservoirs of Permian, Triassic and Jurassic age. Vitrinite reflectances of 700 samples from 44 wells vary from less than 0.4% in the Cretaceous Winton Formation to in excess of 6.0% for some intersections of the Permian Patchawarra Formation. For Burley 1 the vitrinite reflectance is 0.5% at 1658 metres (Lower Cretaceous) increasing to 1.4% at 2013 metres (Middle - Upper Jurassic) and to 6.6% at 3545 metres (Lower Permian). Isorank surfaces (greater than 0.7% Ro) across the main structural low (Nappamerri Trough) are markedly convex upwards. Vitrinite reflectances from the Jurassic sequence in the central part of this trough are higher than those from some more deeply buried Permian sections on the adjacent structural highs. Opposed to this, isorank surfaces less than 0.7% Ro show a positive relationship with depth to basement. The convexivity of the rank surfaces cannot be explained by post-coalification folding. Coalification models in association with present well temperatures indicate an earlier phase of intense coalification in and around the central Nappamerri Trough but most reflectance - depth profiles do not show any marked discontinuity. This early phase of coalification, apparently related to the presence of basement granites, persisted throughout the Permian and, in some areas, until the late Jurassic. Post-Jurassic dewatering of the basin could account for a post-Jurassic increase in temperature over the structural highs. Present geothermal gradients (31oC/km to 58oC/km) are average to markedly above average. The general form of the relationship between coal rank and present temperatures suggests an additional late thermal event which has, so far, had only a minor effect upon coal rank and hydrocarbon maturity.