Senior sulfoxides, such as diethyl sulfoxide (DESO) and ethyl methyl sulfoxide (EMSO), are prospective cryoprotectants. These liquids are either applied in the form of their mixtures with water or mix with water inside the living cell. This work reports vapor-liquid equilibrium (VLE) properties of the senior sulfoxide-water mixtures over an entire composition range. Negative deviations from an ideal behavior were found for both sulfoxides in their aqueous mixtures. The inter-molecular interactions in the mixtures are predominantly electrostatic. A strong hydrogen bond exists between DESO (EMSO) and water, Whereas water does not coordinate the methylene groups. Thanks to their hydrophobic chains, DESO and EMSO exhibit elevated densities at the vapor-liquid interface. Both DESO and DMSO act rather efficiently as surfactants decreasing surface tension of the water-rich mixtures. The reported results confirm stability of the aqueous mixtures of sulfoxides and foster their emerging applications. (C) 2016 Elsevier B.V. All rights reserved.