The Otway Basin is part of the Australian Southern Rift System, formed along Australia's southern margin during a period of rifting and continental breakup which seperated Australia and Antarctica. The northern margin of the basin extends up to 50 miles (80 kilometres) inland while the southern margin is poorly defined and lines in the region of the continental slope some 160 kilometres offshore. Approximately 70 percent of the basin is offshore. The basin straddles the South Australian/Victorian State boarder. The four areas span a variety of structural locations (Fig. 1) and play types, from the northern margin of the Robe Trough (OT95-A), St Clair Trough (OT95-D), Tantanoola Trough (OT95-B) and Voluta Trough (OT95-C). Seismic studies have shown that the stuctural evolution of the Otway Basin is analogous to basins such as the Tucano-Reconcauo Basin of Brazil and the Gabon and Cabinda Basins of the west coast of Africa. Each of these basins have been found to contain at least one giant oil field.