Equilibrium data for the water + 1-butanol + 2-octanol system is determined in this work. Liquid-liquid equilibrium (LLE) data are obtained at 303.15 K and 313.15 K, with a view to investigating the influence of temperature. Vapour-liquid-liquid equilibrium (VLLE) and vapour-liquid equilibrium (VLE) data of the same system are also determined at 101.3 kPa, by means of a modified Fisher Labodest recirculating still that is coupled to an ultrasonic probe. Additionally, the heterogeneous binary azeotrope of the pair water + 2-octanol is determined. Correlation parameters are obtained from the experimental results for use in the universal quasichemical (UNIQUAC) and non-random two-liquid (NRTL) thermodynamic models in CHEMCAD 7. The UNIQUAC, NRTL and original universal functional group activity coefficient (UNIFAC) models are then, in turn, used to predict the LLE and VLLE data from these correlation parameters. (C) 2018 Elsevier B.V. All rights reserved.