The possibility to develop a solubility parameter scale, with the purpose of predicting the performance and help the selection of ILs, is here evaluated. For the estimation of solubility parameters infinite dilution activity coefficient data is used. The results allowed the identification of a curious behavior for the ILs that seem to present more than one solubility parameter acting as polar molecules in some situations and as non-polar molecules in others, depending on the medium. This behavior was confirmed by solubility measurements of [C4MIM][PF6] in solvent mixtures. The solubility parameters were alternatively estimated based on other properties, namely viscosities and enthalpies of vaporization, and the relation between the various sets of solubility parameters is discussed. The results obtained suggest that, given the complexity of IL molecules and their liquid phase, a one-dimensional solubility parameter scale able to characterize these fluids is not feasible.