Isobaric vapor-liquid and vapor-liquid-liquid equilibria were measured for the ternary system water + isopropanol (2-propanol) + isooctane (2,2,4-trimethylpentane) at 101.3 kPa. The experimental determination was carried out in a dynamic equilibrium still, with circulation of both the vapor and liquid phases equipped with an ultrasonic homogenizer. The experimental data demonstrated the existence of a ternary heterogeneous azeotrope at 70.9 degreesC with a composition of 0.31, 0.31, and 0.38 mole fraction of water, isopropanol, and isooctane, respectively.