The relative sound velocities (U-U°) of aqueous NaCl, Na2SO4, MgCl2, and MgSO4 solutions were measured from 0.05m to saturation and from 0 to 45°C. The sound speeds were combined with our earlier work and fitted to a function of molality and temperature to standard deviations within 0.3 m-sec−1. The adiabatic compressibilities, βs, were determined from the sound speeds and used to calculate adiabatic apparent molar compressibilities, Kϕ,s, isothermal compressibilities, β, and apparent molar compressibilities, Kϕ, were determined from the adiabatic values using literature data for expansibilities and heat capacities. The values of Kϕ have been extrapolated to infinite dilution using an extended limiting law. The resulting K0 at various temperatures are in reasonable agreement with literature values. The results of this study have been combined with our earlier results to derive a secant bulk modulus equation of state for NaCl, Na2SO4, MgCl2, and MgSO4 solutions valid from 0 to 50°C and 0 to 1000 bar.