The reserves of crude oil in main geographical regions are presented in the paper. The role of oil in energy mix of the world since the beginning of its exploitation till now is also presented. The analysis of prospects for new oil reserves discovery and exploration is given with emphasize put on the seas and oceans areas. It is stated that 145 thousand millions tonnes of crude oil have been exploited in the history of oil exploitation till the end of 2005. The area of sedimentary basins, where the crude oil reserves have been found constitutes 65% of the total areas of lands and seas that are prospective for discovery of new oil-bearing structures where the minimal oil reserves might be at the level of 107 thousand million tonnes. All together, not taking into account the oil that may be recovered from oil shales and oil sands, it is evaluated that the available amounts for the world will be 165 thousand million tonnes of oil in already documented reserves and 107 thousand million tonnes in perspective areas. From the above stated is seems that assuming the increased oil consumptions in the years to come, the conventional oil reserves should be sufficient at least for the first half of the 21-st century.