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Background: In the present study, vapor-pressures of three geothermal fluids from Baden-Baden geothermal field (Kirchenstollen, Friedrichstollen, and Murquelle, southeastern region of Germany) were measured over the temperature range of 274-413 K. The combined expanded uncertainty of the temperature and vapor-pressure measurements at 95% confidence level with a coverage factor of k = 2 were estimated to be 0.01 K and 1-3 Pa at low and 10-30 Pa at high temperatures, respectively. The measured values of vaporpressure were used to calculate other crucial derived thermodynamic properties of these geothermal fluid samples, such as enthalpy and entropy of vaporization and the heat capacity. Methods: The measurements were performed using two different methods and experimental apparatus: (1) absolute and differential static method which was used at low