The well ILZ Thermal 1 was drilled in the year 1998 to a final depth of 1,906.0 m. Located about 15 km west of the town of Fürstenfeld in the Eastern Styrian Neogene Basin, it perforated Miocene sediments until 1,466.0 m comprising Lower Pannonian to Karpatian sequences. Those are underlain by dolomites of the Graz Paleozoic until 1,906.0 m comprising the basement. Formations were investigated regarding their reservoir characteristics including lithological, hydrogeological and geothermal parameters to define the geothermal system in the area of the well. A focus thereby lies on the Paleozoic basement not only because of highest data density from well logs and cuttings but also because of highest expectable temperatures for geothermal energy utilization. Lower Pannonian and Sarmatian sediments consist of an interlayering of gravels and sands to fine-grained deposits. The Lower Pannonian can be correlated regionally with the “Feldbach-Formation”, whereas the Upper Sarmatian corresponds to the “Gleisdorf-Formation”. Lower to Middle Sarmatian sediments might be correlated with the “Rollsdorf-“ or “Grafendorf-Formation”. Major potential aquifers for drinking water supply are formed by several coarse developed horizons, making up a total aquifer net thickness of 153.8 m with an average resistivity-derived porosity of around 20%. The Badenian series starts with the much finer developed “Bulimina-Bolivina/Rotalia-Cibicides Zone” (BB/RC-Zone). Below, the “Sandschaler Zone” is dominated by coarse sandstones with few shaly to marly intercalations and hence presents major potential for geothermal utilization with temperatures of up to 46.5°C, calculated from a geothermal gradient of 45.5°C/km. Porosities range between 22-25% and transmissivity was calculated to 3.15*10-6 m²/s. The water of the Sandschaler Zone is a sodium-bicarbonate type with a content of total dissolved solids (TDS) of 5.01 g/l. The Sandschaler Zone is underlain by the Lower Badenian Lageniden Zone, consisting of the upper fine and impermeable “Tonmergel Series” and the lower much coarser developed Base Conglomerate, which forms, together with the Karpatian Conglomerate-rich Group, the second important geothermal aquifer. Those are characterized by a more or less very homogeneous very coarse conglomeratic development with minor thin shaly and marly intercalations. However, porosities range between 11-15% and transmissivity was determined to 6.61*10-5 m²/s. The water is typed as a sodium-chloride-bicarbonate water with very high mineralization (TDS=17.9 g/l). Temperatures reach 76.5°C at 1,466.0 m. Finally, the basement is formed by dolomites of the Graz Paleozoic and can be subdivided into three major zones. The upper light to dark gray dolomites and marls (1) are assigned to the “Flösserkogel” Formation of the “Rannach” Facies (Lower to Middle Devonian). Major geothermal potential lies in the uppermost part and around 1,600 m with permeabilities of > 100 mD and 60 mD and temperatures of 76-83°C. The Paleozoic water itself was classified as sodium-bicarbonate type. The lower dark gray dolomites (3) show a very homogeneous development with abundance of breccias increasing towards depth and therefore can be assigned to the Schöckl Facies through correlation with the lower dolomites of the well Arnwiesen 1. Although temperatures reach 96.5°C, those dolomites are not regarded as potential aquifers due to permeabilities of <50 mD. The upper and the lower zone are separated by a fault zone (2), which represents the major structure for convective heat transport in the geothermal system with a permeability of > 260 mD. Geothermal resources can be classified as low enthalpy resources. The temperature range would allow application in agriculture, hot water supply, balneology, radiators, for example.