The speed of sound, and density of the ternary {acetone + methanol + (2-methyl-1-propanol, or 3-methyl-1-butanol)} were measured at T = 298.15 K, and atmospheric pressure. The experimental measurements allowed the calculation of the corresponding derived proper-ties, as well as the analysis of the dependence of the compressibility solvation numbers as a function of concentration. The values of the physical properties were compared with the results obtained by different estimative methods. The role of the branched alcohols in separation distillation sequences for (acetone + methanol) is discussed in the light of the thermodynamic measurements obtained.