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
