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Area A of the Timor Gap Zone of Cooperation has been delineated by the Australian and Indonesian Governments as an area of equally shared administration of, and benefit from, exploration and production of hydrocarbons. Because only one exploration well has been drilled in Area A, little detail is known about its Mesozoic petroleum prospectivity. What is known about prospectivity, resulting from analysis of regional data can, however, be summarised as follows.Regionally, Mesozoic sandstones with petroleum reservoir potential occur in the Middle-Late Triassic, Middle-Late Jurassic and the Late Cretaceous. The petroleum source rock potential of Middle Jurassic to Neocomian shales is expected to be fair to good. The Cretaceous Bathurst Island Formation provides the regional seal.Area A is dominated by the large Kelp strycture on the Western Sahul Platform. However, Jurassic petroleum source rocks like those in the Vulcan Sub-basin are likely to be absent across the Kelp structure and, if present, are likely to be only marginally mature. Mature oil-prone Jurassic source rocks are more likely to occur in the Sahul Trough an-d in the Malita Graben. Consequently, oil accumulations at the crest of the Kelp structure may occur, but would require either long distance migration of oil from the troughs, or migration from deeper and older source intervals, if present.On and near the Kelp feature, faulting is similar to that bounding the small but economic Jabiru and Challis oil fields in the Vulcan Sub-basin region to the south. Assuming similar stratigraphy, the same type of faultblock traps could also occur. Thus the most likely scenario for economic Jurassic oil potential in Area A could be for small to medium sized fields, particularly in traps located near the margins of the Sahul Platform and of adjacent troughs, to which oil could most easily migrate from regions of mature source rocks within the troughs. The target depths are likely to be between 2000 and 3000 m (6500 and 10000 feet).Triassic oil potential may exist but would rely on marine oil- prone source rocks and possible development of reefal complexes on the platform. This would represent a new play. The Triassic sequences in the central parts of the Sahul Syncline and Malita Graben are likely to be over-mature for oil generation and would probably produce gas/condensate.The collision of the Australian plate with the Timor continental block in the Miocene produced compresion, resulting in normal and reversed faults. However, it appears likely that the integrity of the seal associated with the Cretaceous Bathurst Island Formation has been maintained, as indicated by the preservation of the Jabiru and Challis accumulations. This implies th'at Late Creataceous and Tertiary reservoirs are unlikely to be charged with petroleum from Jurassic source rocks, except possibly where unussually large faults cut those levels and allow vertical migration of oil. The Cretaceous and Tertiary source rocks are immature in the region, which downgrades the prospectivity of Late Cretaceous and younger strata.