A study of source-rock richness has entailed the evaluation of TOC data for the Eromanga and Cooper Basins. TOC analyses were averaged and plotted on 1:250 000 basemaps, on a formation by formation basis. The data were contoured by honouring all data points with additional control between wells derived by ghosting off the C' time structure (Sutherland, 1985). TheC-P' isochrons were used in the northern Queensland sector where late structuring has occurred. When shale-thickness and facies maps become available, they will be used as a basis for recontouring the average formation TOCs. 30 foot cuttings samples yielded the most useful TOC data. Core samples represent limited intervals and sidewall cores are point samples, usually shot in shales. Composite cuttings samples, bulked over 300-500 foot intervals, commonly present problems by straddling repicked formation tops. In the Permian, where coal cavings often contaminate cuttings, core and sidewall cores would be more reliable. In general, the data points are sparse, especially for the Westbourne and Poolowanna Formations which have not been identified in many wells. None of the Permian data were contoured because of contamination by coal cavings in many wells. In the Toolachee and Patchawarra Formations lower TOC averages tend to occur over the structural highs and around the margins of the Cooper Basin. Higher TOC values in the terrestrial Eromanga Basin sequence are confined to the zone overlying the Cooper Basin and to northern ATP 259P. Outside these areas the Murta and Westbourne Formations average less than the 0.5% TOC threshold for hydrocarbon explusion (Dembricki and Pirkle, 1985) and are considered to have low potential to generate substantial quantities of oil. Facies developments and associated TOC variations in the Jurassic overlying the southern Cooper Basin reflect the continued subsidence of this area. However, the disposition of the northern Cooper sediments bears little relation to the facies distribution in the overlying Eromanga sequence.