To support plans to expand the current subway network in Vienna to the south, several exploratory wells were drilled along one possible corridor. In one well, gas was encountered in a 20-cm sand layer at a depth of 38 m. The gas-bearing layer is stratigraphically part of zone D of the Pannonian. Detailed information on the stratigraphy of the Pannonian of the Vienna Basin can be found in Friedl (1931) and Papp (1951, 1953). The gas-bearing horizon consists of sand and gravel layers that probably correlate to the braided stream deposits described by Bernhard (1993). In the area where this well was drilled, the subway was planned to come to the surface and continue on elevated tracks. The foundation for the elevated railway section would likely penetrate the gas-bearing horizon. Therefore, it was important to map this horizon to determine its lateral extent and uniformity.