The Stansbury Basin is a relatively unexplored Cambrian sedimentary basin in South Australia. Good quality seismic data has defined a large untested prospect, the Investigator prospect, which has the potential to contain 200 to 300 mmbbl of oil, or 170+ bcf of gas and 4+ mmbbl of condensate. The area is considered to have strong affinities with prolific Late Proterozoic and Cambrian petroleum-producing basins in Central Siberia and the Sultanate of Oman. The Stansbury Basin covers about 4000 square miles and lies partly onshore on Yorke Peninsula and partly offshore beneath Gulf St Vincent, which consists of relatively quiet and sheltered shallow (80-120 feet) waters. It lies in close proximity to the State's capital city, Adelaide (population 1 million), and to refining facilities and an undersupplied market for gas. No exploration wells have yet been drilled in the most prospective section of the basin beneath the waters of the gulf. The main trend of interest is a reef-rimmed platform and shelf margin developed in a back-arc basin, with hydrocarbon source potential from black marine shales occurring in deeper parts of the section to the east. There is abundant evidence to indicate that the reef-like facies are dolomitized with resultant secondary porosity, and that they have remained unbreached since deposition. Other structural plays are present in the form of large, gently dipping anticlinal structures after the style of the giant Siberian fields, plus structures associated with wrench faults. Petroleum exploration carried out to date has been sparse considering the areal extent of the basin. Much of the early effort was based on technologically poor and inadequate seismic data. Exploration has, however, established from shallow onshore well cores and logs that the primary reservoir possesses excellent reservoir characteristics. Drill stem tests conducted in several Yorke Peninsula wells, drilled on doubtful structural closure, yielded traces of gas and highly saline water confirming the integrity of the seal and that no flushing has occurred. The best quality seismic available for mapping was acquired offshore in a speculative survey carried out by GSI in late 1985. The results of this work have been interpreted and form the basis of this proposal. The Investigator Prospect is a drillable structure, delineated in shallow water (80 to 100 feet). The Stansbury Basin tenure comprises Petroleum Exploration Licence 53, awarded on 4 December 1990 to Preview Resources Pty Ltd and Oakman Pty Ltd. PEL 53 covers approximately 10,136 sq. km (2,505,000 acres) and not only contains proven structures but also encompasses all known trends. An exploration programme is in progress which started with a detailed review and the reprocessing of available seismic data. The programme also includes an organic geochemistry evaluation, involving total organic carbon, Rock-Eval pyrolysis, gas chromatography - mass spectrometry and thermal modelling studies. Basement tectonics are also being appraised using potential field data together with reprocessed seismic.