Oil is produced in theAustrian sector of theAlpine Foreland Basin from Eocene andCenomanian reservoirs.Apart frompetroleum, the basin hosts a significant geothermal potential, which is based on the regional flow of meteoric water throughMalmian (Upper Jurassic) carbonate rocks. Oils are predominantly composed of n-alkanes, while some samples are progressively depleted in light aromatic components.The depletion in aromatic components relative to abundant n-alkanes is an effect of water washing.Waters coproduced with oils that are affected by water washing show a progressive reduction in salinity and depletion in 2H and 18O isotopes, indicating that the degree of water washing ismainly controlled by the inflow ofmeteoric water fromtheMalmian aquifer. In some fields with Cenomanian reservoir rocks, a hydraulic connectivity with the Malmian aquifer is evident. However, water washing is also recognized in Eocene reservoirs and in areas where the Malmian aquifer is missing. This shows that existing flow models for the regional Malmian aquifer have to be modified. Therefore, the results emphasize the importance of combining data from the petroleum and geothermal industry, which are often handled separately.