Phase changes in binary systems of poly(ethylene glycol) dodecyl ethers, C12H25(OC2H4)xOH (x=5, 6 and 8) with water have been studied between −40 to 100 ‡C by differential scanning calorimetry. A number of transitions, including the liquidliquid phase separation, were seen and the transition temperatures and enthalpy changes were determined. The observed temperatures were generally in good agreement with reported phase diagrams. In the C12E5 system, three of the four three-phase lines were seen and a more complete phase diagram is suggested for the water-rich part of the system. Most of the phase changes seen above 0 ‡C are accompanied by small endothermic enthalpy changes of 0.7 to 0.9 kJ (mol C12Ex)−1, independent of system studied, type of transition and transition temperature. Water-rich solutions and liquid crystalline phases separate upon freezing into ice and crystals of hydrated amphiphile. Eutectics are developed at the following temperatures and compositions: C12E5 −3.0 ‡C and 54 wt % C12E5; Q2E6 −4.5 ‡C and 54 wt % C12E6, C12E8 −3.8 ‡C and 49 wt % C12E8.