The relative sound velocities (u−u 0) of aqueous HCL, LiCL, NaF, NaCL, NaBr, NaI, NaNO3, NaOH, NaHCO3, Na2SO4, KF, KCL, KBr, KI, KNO3, K2CO3, K2SO4, RbCl, CsCl, NH4Cl, NH4Br, MgCl2, CaCl2, SrCl2, BaCl2 and MgSO4 solutions were measured from 0.01 to 1.0 at 25°C. The sound velocities were fitted to a function of molality (maximum standard deviation 0.05 m sec−1) u=u 0+A m+B m (3/2)+C m 2, where u 0 is the sound velocity in pure water, and A, B, and C are temperature dependent parameters. The adiabatic compressibilities β S were determined from the sound velocities and were used to calculate the adiabatic apparent molal compressibilities φ K (S) of the salts. The φ K and β S of seawater were estimated by using Young’s rule. The calculated values of φ K and β S agree with those determined from the measurements on seawater solution to ±0.18×10−4cm3mol−1bar−1 and ±0.004×10−6bar−1. The sound speeds of seawater calculated from the values of β S estimated from Young’s rule agree on the average to ±0.02m sec−1 (maximum standard deviations 0.07 m sec−1) with the direct measurements of Millero and Kubinski.