The methodology for the study of the liquid-liquid equilibrium of quaternary systems including two inorganic salts, water, and an organic solvent has been reviewed and applied to the water + 1-propanol + potassium chloride (KCl) + cesium chloride (CsCl) system. Mutual solubility, tie-line, and binodal curve data for the quaternary system at (35 and 45) degrees C were measured, and it was found that the effect of temperature on the phase equilibrium was insignificant within the investigated temperature range. Furthermore, the binodal curve data Were satisfactorily correlated using a five-parameter equation, and the experimental tie-line data were compared with values predicated by a modification of the Eisen-Joffe equation.