Aqueous solutions of a homologous series of alkanetriols, from 1,2,3-hexanetriol to 1,2,3-nonanetriol, have been examined with different techniques, including density determination, freezing point depression, and vapor pressure osmometry. Their hydrophobic or micellar parameters were determined at different temperatures (\left(0,20,30\right.), and (\left.40^{\circ} \mathrm{C}\right)) : volumes of monomers or micelles, volume changes during micelle formation, osmotic coefficient, activity of the solute and solvent, nonideal free energy of the solute, and relative chemical potential. (1,2,3-) Hexanetriol does not form micelles and tends to form hydrophobic aggregates at (2.09\left(20^{\circ} \mathrm{C}\right)) and (1.80\left(30^{\circ} \mathrm{C}\right) \mathrm{mol} \cdot \mathrm{dm}^{-3} \cdot 1,2,3-) Heptanetriol is a key compound since it is difficult to speak about clusters or real micellization at (1.03\left(30^{\circ} \mathrm{C}\right)) and (0.98\left(40^{\circ} \mathrm{C}\right) \mathrm{mol} \cdot \mathrm{dm}^{-3}). 1,2,3-Octanetriol and 1,2,3-nonanetriol self associate in a manner similar to that of conventional surfactants. The CMCs respectively obtained are 0.370 to (0.320 \mathrm{~mol} \cdot \mathrm{dm}^{-3}) (temperature range of 0 to (40^{\circ} \mathrm{C}) ) and (0.098 \mathrm{~mol} \cdot \mathrm{dm}^{-3}\left(40^{\circ} \mathrm{C}\right)). Calculations using the phase separation model led to the following values for the aggregation numbers: (2.3 \pm 0.2) for (1,2,3)-hexanetriol, (7.6 \pm) 0.1 for 1,2,3-heptanetriol and (31.9 \pm 0.1) for 1,2,3-octanetriol. The values directly obtained by freezing point depression ( 31.5 (\pm 1.8) ) or vapor pressure osmometry measurements ((27.1 \pm 0.9)) at (40^{\circ} \mathrm{C}) for (1,2,3)-octanetriol show that the phase separation model is thus satisfactorily applied for this compound. The calculated free energy of the micelle formation agrees with published data for similar nonionic surfactants. @1993 Academic Press, Inc.