Abstract Investigations on the thermophysical properties of treated seawater and NaCl, Na 2SO 4 and MgCl 2 solutions of various concentrations have been carried out. Density has been investigated at 20–200°C temperatures and up to 200 bar pressures. The heat conductivity of seawater and solutions of various concentrations was studied at 20–300°C accounting for the solubility and the results analyzed. The viscosity of NaCl solutions was studied by the capillary method at 20–350° C and to 300 bars. The absolute value of viscosity decreases with increase in temperature, but the relative value increases. Heat capacitance of NaCl solutions investigated at 20–200°C, was found to decrease with increase in concentration. The surface tension of NaCl solutions was studied by the method of two capillaries at20–200°C.