The Officer Basin covers some 350,000 square km of central southern Australia, extending from the Yilgarn Block in Western Australia east to the Gawler Craton in South Australia. During the early 1980s Comalco Aluminium Limited explored the eastern Officer Basin for buried deposits of trona (a sodium carbonate evaporite). Their interest followed on from the joint SADME-Comalco identification in 1979 of evidence of an alkali playa lake depositional system for the Cambrian Observatory Hill Formation at SADME's Byilkaoora 1 stratigraphic/petroleum exploration drillhole. Oil shows found within this playa facies in subsequently drilled Comalco mineral exploration holes indicate that within the basin potential exists for hydrocarbon accumulations. Visible oil shows had also been recorded during drill coring of Neoproterozoic rocks underlying the eastern Officer Basin, at Comalco's Marla 9 drillhole. A later fluorescence study of drill cores from this and other drillholes in the eastern Officer area verified and extended the known occurrences of these shows. However, the study was carried out on cores which have laid unsealed in the SADME Core Library for a decade. The geologically more mobile light hydrocarbons would thus have disappeared.