Analysis of geological positions of the largest oil-and-gas-bearing basins, carried out on the basis of research data represented in the “Geological atlas of Russia” and other publications, allowed to mark out petroleum-bearing Ural-African oil and gas belt. This largest on the Earth belt of hydrocarbons accumulation is connected with the near-meridional band of a giant long-existing intercontinental faulting (rifting) zone preexistent since Riphean in the central part of Eurasia and elongated with smooth rejuvenation through Paleozoic and Mesozoic into the South Caspian region, Persian gulf and into African platform (meridian system of African rifts). Most part of conventional oil (near 75%) and gas (more than 65%) reserves are concentrated within the bounds of this belt. The area of this unique “saturated-in-hydrocarbons” structure makes only 6-7% of the total globe surface. By its geological structure and character of the mantle and crust masses differentiation, this belt features the global anomaly zone in the Earth gravitation field. Large part of the Ural-African transcontinental petroleum belt (>50% of area) occurs on the territory of Russia. Its northern part comprises principal Russian oil-and-gas-bearing basins comprising most of large and super-large hydrocarbon fields which contain predominant amount of explored in Russia reserves of oil (95%) and gas (>95%). By the thickness and area size of sedimentary cover, as well as the quantity of explored natural gas resources, the West-Siberian basin is quite similar to the Persian Gulf significantly receding only in oil reserves (8 times less). Taking into account a certain parity of oil and gas ratio in principal petroleum basins of the world, the revealed oil-gas disproportion in West Siberia may be considered as an argument for high probability of new discoveries of oil fields there.