Speeds of sound, densities, and refractive indices of the ternary mixture acetone + methanol + ethanol have been measured at 298.15 K and atmospheric pressure. The excess molar volumes, changes of refractive indices, and isentropic compressibilities were determined from the experimental data. Several methods for predicting multicomponent derived properties from binary data were tested. The Peng-Robinson and Soave-Redlich-Kwong equations of state were also applied, with three different mixing rules, to calculate binary interaction parameters and predict ternary excess volumes, satisfactory results being obtained for this mixture.