The apparent molar volumes V φ of aqueous R-alanine, β-alanine, and proline have been determined with platinum vibrating tube densitometers at temperatures from 298 to 523 K and at pressures in excess of steam saturation. Values of the standard partial molar volumes V°for the aqueous amino acids increase with temperature then deviate toward negative values at temperatures above 398 K, consistent with a lowering of the critical temperature in the solutions relative to water. This is opposite to the behavior predicted by the correlations developed by Shock and Helgeson (Geochim.