A review of existing information indicated the possibility of Permian sediments extending southwards beneath Mesozoic cover. During 1971-1972, the licensee completed 10 rotary drilling traverses across strike that covered the entire Phillipson Trough, apart from its NW sector, where the proposed Commonwealth Railways line linking Kingoonya to Alice Springs was to be constructed. This drilling disclosed a Permian intracratonic sub-basin extending NW-SE that measures 30 miles by 3-5 miles, and is surrounded by concealed basement rocks. After drilling 66 holes, it was discovered that 10 major coal seams (A to J) of sub-bituminous rank brown coal, the thickest ranging between 10 and 15 feet thick, subcrop within the Permian Mount Toondina Beds over 90 square miles in the centre of the the trough, together with several lesser seams 1 to 4 feet in thickness. At the W and S periphery of the Phillipson Trough the number of coal seams and their thickness decrease, and coal is missing from its eastern side. However, 2 reconnaissance drillholes that were put in about 9 miles W of the main part of the trough encountered what presumably was another Permian sub-basin, again containing 10 recognisable coal seams, one of which was 17 feet thick. Analyses of numerous coal samples showed a low rank, high volatile coal with moderately low ash and sulphur content, which is relatively consistent in quality. Frequent mudstone band splits in the major coal seams are too thin to be efficiently extractable, so the economic assessment had to embrace the concept of multiple seam mining. The major coal seams mostly occur shallower than 400 feet below surface. A preliminary strip mining feasibility study was carried out. Using a 250 foot highwall as a nominal limit for strip mining, 180 million tons of 'F' seam coal were proven in the Main Basin area. 100 million tons were indicated in the next overlying 'P-A' seam, based on its main ply only, which occurs shallower than 250 feet. Follow-up drilling of the West Basin coal discovery during mid 1973 (29 holes) demonstrated that the 7 main seams are buried beneath a maximum of 162 feet of Mesozoic overburden, and contain indicated mineable reserves of 330 million tons of coal. Another 45 holes drilled in the NW of the Main Basin completed the delineation of that deposit, and established its relationship with the West Basin. It was concluded that due to the overlap of the Main and West basin deposits' seams, strip mining to a 250 foot highwall could possibly be extended over the whole Lake Phillipson coalfield almost without a break, to cover an area of 12 by 22 miles. Continued pre-development drilling of both deposits during 1973- 1974 proved an hypothesis that the Lake Phillipson Trough Main and West sub-basins converge at their northern limits and then turn west to join the Wallira Trough. Gross coal reserves of 3000 million tons are now estimated to exist.