Twenty samples of potential source rocks from formations of the Molasse Basin, of which some are from identical formations, but different depths, were selected from the stores of oil companies. The pulverized sample materials were treated with org. solvents, followed by demineralization of the insol. residues to obtain the kerogen fractions. The exts. were sepd. by liq. chromatog. The stable C isotope ratios of the ext. fractions and those of the kerogens were detd. The bore cores from the West Molasse are not distinctly related to the corresponding crude oils. In the East Molasse, there exist isotopic relations in the case of the Rupelian and the Sannoisian samples which do not preclude the characterization of these formations as potential source rocks. As the samples investigated are too immature for the prodn. of oil, more mature source rocks may occur in larger depths, near the southern margin of the basin. According to theor. and exptl. considerations, only an insignificant enrichment in 13C in kerogen is to be expected with increasing metamorphism; therefore, isotopic correlation methods can be applied to immature kerogen samples with some success.