Liquid-liquid equilibrium (LLE) tie-line compositions were measured for the binary system iodine-water and the ternary system hydrogen iodide-iodine-water (HI-I-2-H2O) at 199.1 and 252.2 degrees C, at pressures of 60 bar, conditions of interest for the reactive distillation column of the Sulfur-Iodine Cycle. To keep the HI decomposition reaction negligible, a continuous-flow apparatus was used to minimize residence times at the elevated temperatures. Sixteen equilibrium tie lines were measured, using overall feed compositions ranging from 0.0 to 3.3 mol % HI, and the plait-point composition for 199.1 degrees C was estimated. Sample compositions for the lighter, water-rich phase and the heavier, I-2-rich phase were both determined via titration of HI and I-2, with water being obtained by difference. The phase behavior indicates that the selectivity of HI for the aqueous phase can be large, ranging from 10 to 100+ for tie lines removed from the critical region. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.