The densities and refractive indices of water + methanol + 2-methoxy-2-methylpropane mixtures were determined in the miscible region at 298.15 K and atmospheric pressure. The densities were used to calculate excess molar volumes for the ternary mixtures and for methanol + 2-methoxy-2-methylpropane mixtures. Redlich-Kister polynomials were fitted to the excess molar volume results.