Nineteen core samples of potential source rocks for crude oils in the Eastern Molasse Basin were investigated with respect to their isotopic compn. of stable C in org. exts. and kerogens. Some of the chem. and isotopic results give pos. or neg. indications for the relations between crude oils and the selected core samples. The anal. data point to the clayish sediments of the Rupelian and Sannosian as probable source rocks. These samples were proved to be of low maturity by their elemental compn.