Methanol is a potentially important impurity in subsurface oceans on Titan and Enceladus. We report measurements of the freezing of methanol‐water samples at pressures up to 350 MPa using a volumetric cell with sapphire windows. For low concentrations of methanol, the liquidus temperature is typically a few degrees below the corresponding ice freezing point, while at high concentrations it follows the pure methanol trend. In the Ice‐III regime, we observe several long‐lived metastable states. The results suggest that methanol is a more effective antifreeze than previously estimated and might have played an important role in the development of Titan's subsurface ocean.

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