A simple expression to evaluate the isothermal compressibility, adiabatic compressibility and sound velocity of liquid mixtures from excess volumes, considerably improving the predictions from ideal mixing rules, is proposed. This equation is based on the exclusion of 'incompressible' volumes for the calculation of compressibilities. The incompressible volumes of different compounds have been estimated by fitting the compressibility of binary mixtures. Consistent values have been found for all the substances analysed. The incompressible volumes obtained are compared to the excluded volumes of similar approaches. (C) 2009 Elsevier B.V. All rights reserved.