Eleven samples of crude oil from the Molasse Basin of southern Germany were fractionated and their contents of S and N as well as the stable isotope compns. of these elements (34S/32S and 15N/14N, resp.) investigated. According to d34S detns., all Tertiary crude oils of the western and eastern Molasse belong to 1 oil family and differ significantly from the Triassic and Liassic oils in the western Molasse. An enrichment of 34S was obsd. with increasing polarity of crude oil fractions. The isotope distributions of S in the polar constituents of the biodegraded oils from the sandstones of Ampfing, however, approach a homogeneous distribution. The N isotope distribution is rather uniform in southern German oils. A regional differentiation can be recognized, although the overall isotopic variation is small. The d15N values of the crudes and asphaltenes could not be correlated.