BHPP's Greenly 1 well is herein proposed to test a faulted hanging wall anticline with minor crestal collapse faults, an estimated fault-dependent maximum closure area of 53.3 square km, and a closure height of 140 metres at the primary target. The trap formed during the Late Cretaceous. Primary target reservoir sands of the Late Cretaceous Wombat Sandstone Member are estimated to be 71 metres thick, with an average porosity of 20% and good permeability. They are sealed by the Late Cretaceous Wigunda Formation (Fm.) mudstones, and will be reached at a depth of 2704 metres subsea. Secondary, higher risk targets exist above and below the primary target level. Hydrocarbons are interpreted to have been generated from the Early Cretaceous upper Borda Fm. source rocks in the Outer Sub-basin, which entered the oil window during the Late Cretaceous. The main period of migration into the trap occurred during the Late Cretaceous and Tertiary via conduits in the Ceduna and Platypus Fms. Greenly 1 will be the second well drilled in the Duntroon Basin by BHP Petroleum in 1993, and the first well to test a valid structure within the Cretaceous sequence. The risk factors are encouraging for a frontier basin play, and are 7% for 'chance of hydrocarbons' and 5.5% for 'chance of oil'. Source and migration are assessed as the greatest risks. The Greenly 1 well will test an area of the basin considered to have the best chance of hosting liquid hydrocarbons. An included table summarises the volumetrics at the primary target and secondary target levels.