Densities of binary mixtures of diethylsulfoxide (DESO) with water and dimethylsulfoxide (DMSO) with water have been measured over the full range of compositions at temperatures from 298.15 K to 343.15 K by means of a vibrating-tube densimeter. The excess molar volumes V-m(E), calculated from the density data, are negative over the whole range of composition and temperature. The V-m(E) curves exhibit a minimum at about x congruent to 0.4. These data conform with those for dimethylsulfoxide (DMSO + water) system known from literature at different temperatures as well. Our data additionally confirm that very strong interactions take place between DESO and water, even stronger than those between DMSO and water. This behaviour could explain the strong deviations from the ideality observed in this system. The V-m(E) results were correlated using a modified Redlich-Kister expansion. The partial molar volumes increase with increasing mole fraction and temperature. The excess partial molar volume of sulfoxide at infinite dilution, V-2(E infinity), at each temperature (DMSO + H2O) and (DESO + H2O) mixtures is positive. For (DESO + H2O) system the dependence of the expansion coefficient against mole fraction of DESO reveals a maximum which is additionally supports the hypothesis of a strong (DESO + water) interactions. (c) 2004 Elsevier Ltd. All rights reserved.