Packsaddle is an arcuate, north-east trending anticline, 48 km long, which is fault bounded along its north-western and south-eastern flanks. It is one of the major anticlinoria along the Gidgealpa-Merrimelia-Innamincka anticlinal Trend. At the level of the 'Z'-Horizon, the throw on the major north-western fault is up to 3000 feet. The culmination exhibits about 1000 feet of vertical closure, but 800 feet of that is reliant upon fault closure. Packsaddle West Prospect contains 560 feet of prospective section in the Patchawarra Formation, of which 50 feet could be Net Effective Pay. The anticipated total depth of a test well is 9360 feet. The target Permian section thins considerably across the structure, to a currently interpreted minimum thickness of 400 feet, but it may be entirely absent along the anticline crest. This loss of section is due primarily to massive mid-Permian erosion, but may also be due to limited or non-deposition during the Late Permian. Therefore the Permian section which is likely to be encountered by the drill consists of possibly the Toolachee Formation, lowermost Patchawarra Formation, possibly the Tirrawarra Sandstone, and the Merrimelia Formation. The major plays predicted in the Patchawarra Formation are unconformity traps. The expected trapping mechanisms for the Tirrawarra Sandstone and Toolachee Formation, if present, will be anticlinal or pinchout. The proposed well location and rationale is a tentative one only and the prospect requires further study before a definite site is located. To date only one test well, Packsaddle 1, has been drilled, which contained gas despite the fact that it was located some distance downdip on the eastern flank of the structure. The proposed site of Packsaddle West 1 is more than 23 km west of Packsaddle 1, and is separated from it by a system of at least three major faults. Packsaddle West is thus a different prospect from that drilled by Packsaddle 1. Ultimately, because of the anticline's size, and its complicated structure, a number of wells will need to be drilled on and around Packsaddle. Examples of prospective sites for wells include one updip from Packsaddle 1, one at the crest, others on the western and north-eastern flanks, and one on the northern, downthrown side of the major bounding fault. The well at Packsaddle West is being proposed to form part of the 1978 Independent Exploration Programme to be carried out on behalf of PASA. Delhi will be the operator. Ownership of any petroleum discovered will remain with the partners to the Merrimelia-Innamincka Farmout agreement.