Liquidi in the system H2O+NaCl were determined experimentally for bulk compositions of 5, 10, 15, and 25mass% NaCl at pressures to ∼1.4GPa using a high-pressure optical cell or a hydrothermal diamond-anvil cell combined with Raman spectroscopy. The dP/dT slope of the ice I liquidus becomes steeper with increasing salinity, i.e., it decreases from ∼−9MPa/°C for pure H2O, to ∼−11MPa/°C for 5 and 10mass% NaCl, and to ∼−15MPa/°C for 15mass% NaCl. The liquidi for other solid phases at higher pressures always display a positive dP/dT slope. The liquidi of 5mass% NaCl have dP/dT slopes similar to those of the corresponding ice melting curves of pure H2O, but the ice stability fields shift towards higher pressures, e.g., the ice I+ice III+liquid triple point was observed at ∼300MPa and −27.7°C (that of pure water is at 209.9MPa and −21.985°C). At 15mass% NaCl, a hydrohalite liquidus replaces the ice III and ice V liquidi, and also decreases the range in pressure of ice I stability. Approximate P–T locations of triple points for 15mass% NaCl are ∼1.07GPa and 1.7°C for hydrohalite+ice VI+liquid, and ∼25MPa and −11.7°C for ice I+hydrohalite+liquid (for comparison, the ice I+hydrohalite+L+V quadruple invariant point is at −21.2°C, ∼0.0001MPa, 23.15mass% NaCl). The stability field of ice VI shifts continuously towards higher pressure with addition of up to 25mass% NaCl, with probably only small changes in the dP/dT slope of the liquidus. At 25mass% NaCl, the hydrohalite liquidus extends from 0.1MPa to higher pressure and shows a change in the dP/dT slope from negative to positive at ∼−7.5°C and ∼140±40MPa, which suggests a change in the dynamic structure of the aqueous liquid.Raman spectra of an unknown phase of columnar crystal habit are reported, which formed upon freezing of 15 or 25mass% NaCl solutions at high pressure. The Raman spectrum of this phase in the O–H stretching region is characterized by three bands at ∼3410, ∼3460, and ∼3510cm−1, and does not match any of the ice phases or hydrohalite.Based on the liquidi in the H2O+NaCl system determined in this study and a calculated temperature profile from the literature, the icy shell overlying an aqueous liquid mantle on the Jovian satellite Europa is estimated to be about 9km thick, assuming NaCl as the predominant solute. Furthermore, our liquidus data suggest a maximum NaCl concentration of about 15–20mass% NaCl and a minimum subsurface ocean temperature of ∼260K.