Experimental isobaric vapor-liquid-liquid and vapor-liquid equilibrium data for the ternary system water (1) -cyclohexane (2) -isooctane (3) and the quaternary system wafer (1) -ethanol (2) -cyclohexane (3) -isooctane (4) were measured at 101.3 kPa. An all-glass, dynamic recirculating still equipped with an ultrasonic homogenizer was used to determine the VLLE. The results obtained show that the system does not present quaternary azeotropes. The point-by-point method by Wisniak for testing the thermodynamic consistency of isobaric measurements was used to test the equilibrium data.