A new calorimetric method and the results of determination of binary systems phase equilibria having a region of phase stratification on the basis of calorimetric measurements are described in this paper. Isochoric heat capacity temperature dependence of binary system of hydrocarbon-water has been studied by the method of high-temperature adiabatic calorimeter. Parameters of the phase stratification region have been determined on the basis of revealed peculiarities of this dependence at phase transitions liquid-liquid and liquid-vapour and phase diagram have been made.