The data are the background database of The European Geothermal Fluid Atlas. The dataset was generated by the Horizon2020 project REFLECT (Redefining geothermal fluid properties at extreme conditions to optimize future geothermal energy extraction). The aim was to help operators to assess what kind of fluids might be expected at a certain location, and thus have an improved view of the associated risks when installing a geothermal power plant. Fluid data have been collected from 21 European countries. If available, data of corresponding wells, rocks, and reservoirs were also integrated. The focus was on fluids used for electricity generation (> 100 °C), but some data from heat projects were included, too.