Crude oils derived from the Alpine foreland are divided into 4 groups according to their org. chem. compns. and their ratios of stable C isotopes (2 groups in the west, 2 groups in the east). In the west, one group consists of Triassic and Jurassic oils in the North of Lake Constance (source rock: perhaps Mushelkalk). The oils derived from the Bausteinschichten (Lower Chattian) and that from Tettnang 1 (found in the bituminous Helvetian facies of the Malm) belong to the second group. This result points to Malm as a probable source rock for crude oils from the Bausteinschichten. In the east, a western group (E I) consists of deep-seated oils derived from the Tertiary base southeastern Munich (source rocks: perhaps Malm with Upper Cretaceous or Sannois). An eastern group (E II) is represented by the oils (Tertiary base) of shallow depth from Muehldorf-Velden (source rocks: perhaps Upper Cretaceous, maybe together with Malm). Biodegrdn. of the crude oils may be indicated in E II and explained by the transport of bacterially formed gases from above to the Tertiary base by down-streaming pore waters. This mechanism is considered possible in E II only.