The speed of sound and density of aqueous solutions of CoCl2 and CoBr2 were measured at concentrations ranging from (0.1 to 2) mol . kg(-1) and within the temperature limit (291.15 to 297.15) K. The dependences of the adiabatic compressibility coefficient, kappa(S), the apparent molar compressibility, Phi(KS), and the apparent molar volume, Phi(v), on concentration and temperature were determined. The corresponding partial molar quantities were found by extrapolation to infinite dilution.