Heterosegmented statistical associating fluid theory (SAFT) is developed to model the thermodynamic properties of aqueous imidazolium ionic liquid solutions. A set of transferable parameters is obtained, and in general, the model well represents the density, the activity coefficients, and the osmotic coefficients of aqueous ionic liquid solutions. This heterosegmented SAFT, coupled with the Van der Waals and Platteeuw theory for hydrate phase, is also found to well predict the methane hydrate dissociation conditions in the presence of imidazolium ionic liquids and well captures the roles of pressure, anion type, alkyl length of the cation, and ionic liquid concentration on the hydrate inhibition performance of the ionic liquids. (C) 2013 Elsevier Ltd. All rights reserved.