As entry for the 6th industrial fluid property simulation challenge, the COSMO-RS method in its COSMOtherm implementation has been used to predict the mutual solubilities of dipropylene glycol dimethyl ether (DPGDME) and water. The miscibility gaps and their unusual inverse temperature dependence have been qualitatively correctly predicted with COSMOtherm standard procedure. For quantitative agreement some adjustments based on experimental data at 298 K turned out to be necessary. Fine timing of the water and DPGDME areas led to a good quantitative agreement with experimental data with a maximum deviation of 5.4 mass percent points, which turned out to be the most accurate predictions within all challenge submissions. (C) 2011 Published by Elsevier B.V.