New consistent vapor-liquid equilibrium (VLE) data for the binary system methyl I,1-dimethylpropyl ether (TAME) + 2,2,4-trimethylpentane (isooctane) and the ternary system 2-methyl-2-propanol (TBA) + methyl 1,1-dimethylpropyl ether (TAME) + 2,2,4-trimethylpentane (isooctane) are reported at 101.3 kPa. In the binary system, the results indicate a positive deviation from ideality and no azeotrope is present. The ternary system presents a saddle point azeotrope that can be predicted from binary data. The activity coefficients and boiling points of the solutions were correlated with their composition by Wilson, UNIQUAC and NRTL equations.