The preferential solvation parameters for the mutual association of acetonitrile with a co-solvent in their binary mixtures and for the self-association of acetonitrile in these mixtures, and the self-association of each of these components at infinite dilution in the other component as solvent have been determined. The co-solvents studied include dichloromethane, acetone and nitromethane that form practically ideal mixtures with acetonitrile and 1,2-dichloroethane and chloroform that nearly do so, as well as benzene, toluene, chlorobenzene, tetrarchloromethane, methanol, ethanol, acetic acid, formamide, dimethylformamide, and dimethylacetamide, which show appreciable preferential solvation. (C) 2019 Published by Elsevier Ltd.