ABSTRACT: N.V- Lopatin, a Savlet scientist, has faııml that the relation between the-Temperaturo-Index (I) and vitrinite reflectance may be outlined by the formula u>f Bö = 1,301 lg I - 0,5282. In this way it has been possible to calculate the vitrinite reflectance which shows the degree of maturity of the source rock. The calculated vitrinite reflaetanee may be used for estimating the quantity < f n, troleum produced by the »ource rock in a basin which has not been previously drilled.