Liquid-vapor critical temperatures (tc) have been determined visually for a variety of single electrolyte aqueous solutions at several molalities up to 1·5–2·5. The dissolved electrolytes studied were LiCl, NaCl, KCl, KBr, KI, CsNO3, KHSO4, NH4Cl, NH4HCO3, (NH4)2CO3, (NH4)2SO4, CaCl2, MgCl2, Mg(NO3)2, HCl, HClO4, HNO3, CH3COOH, H2SO4, H3PO4 and H3BO3. The alkali halide solutions produced the greatest increase in tc from that of pure water (tc = 374.2°C) where at 2 m all values of tc were in the range of 450 to 480°C, providing an increase of +80 to +110°C. Several of the acids (H2SO4, H3PO4, H3BO3) and divalent salts (CaCl2, MgCl2, Mg(NO3)2, (NH4)2SO4) showed intermediate increases, while particular solutes (HCl, HClO4, (NH4)2CO3, NH4HCO3, CH3COOH) gave very little change from tc for water. It is suggested that these differences in behavior are related to differing electrolyte association, hydration, ion size, decomposition for particular electrolytes (HClO4), and other properties.