The Zala basin is a subbasin within the Pannonian basin of Hungary. Oil and smaller amounts of gas are produced from Upper Triassic through Miocene reservoirs. Our geochemical study of oils and rocks in the basin indicate that two, and possibly three, genetic oil types are present in the basin. Miocene source rocks, previously believed by explorationists to be the predominant source rock, have expelled minor amounts of hydrocarbons. The main source rock is the Upper Triassic (Rhaetian) Kossen Marl Formation or its stratigraphic equivalent. Oils derived from the Triassic source rock are recognizable by their isotopic and biological marker composition, and high content of metals. In other areas of Europe, Upper Triassic source rocks have been correlated with large oil accum lations (e.g., Molassa and Villafortuna fields, Po basin, and other fields in Italy) or are postulated to be good potential source rocks (e.g., Bristol Channel Trough). Knowledge of the geochemical characteristics of oils derived from these Upper Triassic source rocks and understanding of the source rock distribution and maturation history are important for recognizing Triassic oil-source bed relationships and for further exploration in other basins in Hungary and other parts of Europe where Triassic source rocks are present.