The inverse Kirkwood-Buff integral (IKBI) approach is applied to the preferential solvation of F-, Cl-, Br-, I-, and ClO4- in aqueous mixtures of the co-solvents (S) methanol (MeOH), ethanol (EtOH), t-butanol (t-BuOH), 1,2-ethanediol (EG), glycerol (Gly), acetone (Me2CO), acetonitrile (MeCN), formamide (FA), N,N-dimethylformamide (DMF), N,N,N',N',N '',N ''-hexamethyl phosphoric triamide (HMPT), and dimethylsulfoxide (DMSO), as far as the relevant data exist in the literature. Fluoride anions are selectively solvated by the water up to large mole fractions (x(s) >= 0.4) of S = EtOH, t-BuOH, Me2CO, MeCN, and DMF, and up to lower contents (x(s) similar to 0.1) of MeOH, EG, FA, and DMSO. The other anions are preferentially solvated by water to diminishing extent as their sizes become larger, and the largest ones show some preference for S in water-rich mixtures of MeOH and FA, whereas in aqueous Gly even chloride is preferentially solvated by the Gly. The competition between the co-solvent and the anion for the hydrogen bonds that water molecules donate is the main cause for the observed preferential solvation behaviour. (c) 2007 Published by Elsevier Ltd.