Abstract Experimental liquid–liquid phase diagrams have been obtained for five-component systems containing 2,2,4-trimethylpentane (isooctane), benzene, methanol, water, and sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT), at 298.15 and 308.15 K. The density and interfacial tension of conjugate phases whose equilibrium concentration is located on the isothermal binodal curve have also been experimentally determined at 298.15 K for the five-component systems. The phase diagram is of type II when the multicomponent system has 5 mass% of AOT. The overall miscibility of the system is enhanced with 15 mass% of AOT, at 298.15 K, hence the phase boundary decreases and the phase diagram changes to type I. Both the density of each conjugate phase and the interfacial tension of each tie-line are valuable indicators of the degree of miscibility of the multicomponent systems. Water solubility in the hydrocarbon-rich phases is greatly increased due to the formation of reverse micelles with AOT. The experimental tie-lines results were regressed with the NRTL and UNIQUAC solution models with satisfactory quantitative reproduction of the results.