Two vibrating tube densimeters have been used to measure the densities of two mixturesswater + diethanolamine + methanol and water + N-methyldiethanolamine + methanolsin the temperature range (283 to 353) K. The alkanolamines and methanol contents are respectively (between 20 and 50 and between 20 and 60) mass %. The experimental results have been correlated using the Redlich-Kister equation for the excess volume. A set of parameters for the Redlich-Kister equation has been determined using the densities of pure compounds and of binary systems available in the literature. The methodology has been extended to density calculations dealing with hybrid solvents.