This study describes a new method for quantification of hypothetical oil and gas resources, which is considered to be an alternative to conventional estimates by analogy to geologically similar plays and is most appropriate for maturely explored provinces. This method is based on the size–frequency distribution of oil accumulations in sedimentary basins and has never been applied to petroleum exploration. The new approach makes it possible to assess the oil resources concentrated in small and smallest oil fields, which may become the main targets for petroleum exploration. This study reviews the discovery and exploration history of the Volga–Ural province and provides estimates of initial and hypothetical oil resources and the size distribution of undiscovered field and the number of their pools. It was shown that given the volume of exploratory drilling of 500–550 thousand m per year, it is expected that more than three billion tons of oil would be produced from small and smallest fields of this province by the mid-21st century, with a stable annual production of 40–50 million tons. It was shown that the development of small and smallest oil fields is performed by small and medium-sized oil companies, which can be delivered through a dedicated government program.