The experimental equilibrium tie-lines of two quaternary mixtures for (methanol + 1,1-dimethylpropyl methyl ether + toluene + 2,2,4-trimethylpentane) and (methanol + 1, 1-dimethylethyl methyl ether + toluene + 2,2,4-trimethylpentane) were measured at the temperature 298.15 K and ambient pressure. The quaternary experimental results and their constituent ternaries have been satisfactorily predicted using binary parameters alone obtained by an associated-solution model that takes into account association of methanol molecules and solvation between (methanol + polar molecules) with allowance for a non-polar interaction given by an extended form of the UNIQUAC model. The results are further compared with those correlated by modified and extended forms of the UNIQUAC models that include multi-body interaction parameters in addition to binary ones. (c) 2005 Elsevier Ltd. All rights reserved.