This study has concentrated on mapping Unit-defined reservoir distribution trends within the Patchawarra Formation and Tirrawarra Sandstone in the central Patchawarra Trough. Recognition of these trends will impact on the exploration potential of the study area in three categories: (a) existing leads and prospects; (b) appraisal and exploration around existing fields; and (c) stratigraphic plays. The mapping process was based on facies modelling and regional gross and net sand calculations. The Patchawarra Formation was reviewed in the context of a 5-fold stratigraphic subdivision based on regionally correlatable coals, while the Tirrawarra Sandstone was treated, in a regional sense, as a sheet sand. The reservoir potential of the Patchawarra sub-units summarises both facies and structural controls, and reservoir distribution is shown on net and gross sand maps. Reservoir potential decreases from the southwestern portion of the study area to the northeast due to a combination of: 1. a thinner sedimentary section with reduced gross sand; and 2. lower net/gross sand ratios due to both depth of burial and facies variations. Overall, the predicted gas potential of existing prospects has increased as a result of higher net sand counts. Inspection of existing fields (Patchawarra reservoirs) reveals that most are filled very close to spill point, and hence possible gas is generally restricted to a halo around the edge of structures, thereby often negating the need for appraisal drilling. Stratigraphic plays, at the Patchawarra level, have been considered in the context of net sand development in crestal locations combined with the degree of down flank thickening related to structural growth. The aim is the definition of down flank traps with viable reservoir development. The most favourable reservoirs (fluvial) occur in the 'V2' - 'Vc' interval which should be targeted for down flank stratigraphic plays. Conversely, the 'V' - 'V2' and 'Vc' - 'W' isochrons relate to predominantly delta plain facies with relatively sparse reservoir development. Reservoir development in the Tirrawarra Sandstone is closely related to gross sand development and depth of burial. Gross sand thickness is closely related to formation thickness, while net sand trends are controlled by a combination of gross sand development and structure. An additional consideration is how to predict the degree of inhibition of diagenesis within these reservoirs that is caused by the presence of hydrocarbons, since this has been shown in existing fields to lead to porosity and permeability preservation above the hydrocarbon-water contact. One of the principal aims of this study was to determine whether the Tirrawarra fluvial system which deposited reservoir quality sands in the central Patchawarra Trough area was also active in flank areas. Efforts have been hampered by a dearth of well information and by the fact that seismic offers little assistance, owing to poor definition of the Tirrawarra Sandstone seismic response and the large distances between well ties. However, it is concluded that several wells have intersected possible Tirrawarra facies on the western flank of the trough. The well data is corroborated in part by some of Santos' most recent seismic mapping, which indicates that the Tirrawarra zero edge is largely erosional on this western flank, thus implying that the Tirrawarra palaeodepositional edge was actually once located beyond the current Cooper Basin margin. Hence reasonable quality Tirrawarra reservoirs could be expected to persist as far as the very margin of the present basin, although this supposition has still to be verified by drilling. Within the study area a number of fields occurring on highs in the central trough area (e.g. Tirrawarra, Fly Lake) are largely filled to spill point, which suggests that continued updip migration of hydrocarbons into structures on the trough flanks is a strong possibility. The major remaining constraint to the existence there of valid plays is the need for ongoing seismic work to convincingly demonstrate the presence of a viable trapping mechanism.