Gibbs‘ free energies of transfer of halide ions from water as reference solvent to the complete range of water and dimethyl sulfoxide mixtures from various data sources have been used to give the compositions and amounts of the contributing solvation states X(H₂O)j(Me₂SO)_k. The results are discussed with respect to existing results on the hydration of these ions and to known properties of water and dimethyl sulfoxide mixtures.