The Nepa-Botuoba Region forms part of the large Lena-Tunguska Petroleum Province of the Siberian Platform. It is the most prospective area of the platform and covers 300.000 sq km of its southeastern portion. Extensive geological and geophysical investigations and the drilling of over 900 exploration wells have led to the discovery of 22 oil and gas fields. Of these, 7 are considered are large. In addition to discoveries, a considerable number of prospects has been identified. The region encompasses the Nepa-Botuoba Anteclise - a major uplifted element of the Siberian Platform. This feature has an elliptical outline with its long axis trending southwest-northeast. The Anteclise is surrounded by large depressions. The rocks of the Nepa-Botuoba Region include a crystalline basement with a cover of shallow-water and continental platform sediments ranging in age from Middle Riphean (Late Proterozoic) to Jurassic. Total sediment thickness is about 2 km in the crustal area of the Anteclise. The bulk of the section, which also contains all known hydrocarbon deposits, is of Vendian (latest Proterozoic) and Lower Cambrian age and consists of clastic sediments and shelf limestones. These, in the Lower Cambrian, are interbedded with thick evaporites. Basic dyke and sill intrusions of mainly Triassic age are locally important. Structurally, the Anteclise is characterized by gentle warping and block faulting; minor thrust structures have been observed near the southeastern margin. The main source rocks in the Nepa-Botuoba Region are Riphean shales preserved in the depressions surrounding the Anteclise. Of particular importance is the Predpatom trough in the southeast which is considered as the most prolific zone of hydrocarbon generation. Vendian source rocks are less enriched but more widespread. Principal reservoirs are Lower Vendian sandstones and Upper Vendian carbonates which lie under very efficient Lower Cambrian evaporite seals; additional reservoirs are formed by intra-evaporite carbonates of Lower Cambrian age which locally include important reef bodies. Predominant trap types are tilted blocks, domal uplifts and gently faulted anticlines. Accumulation of hydrocarbon appears to have taken place in Cambro-Ordovician times when, in the neighbouring paleotroughs, much of the source material had reached the oil window or (in the deepest part of the Predpatom trough) the zone of gas generation. Except the Irelyakh field in the northeast of the Region, hydrocarbon production has yet begun in any of the fields of the Nepa-Botuoba Region. Of most importance for oil production appears to be the Verkhnechona and Srednebotuoba fields where the annual estimated that - if suitable investment were available - production could reach 15 million tons by the year 2015. Plans exist for the construction of the necessary refineries and of oil and gas pipelines to Ust'-Kut and lrkutsk.