Vapour-liquid equilibria of ionic liquid - carbon dioxide systems, as well as thermo-physical properties of the system components are very important to design and optimize various separation and reaction processes. In this work the solubility of carbon dioxide (CO2) in trihexyl(tetradecyl)phosphonium bromide([THTDP][Br]) was measured using a high-pressure sapphire cell, in pressure range of 8-22 MPa and at two temperatures, 313.2 K and 323.2 K. The thermophysical properties, namely liquid density and surface tension of the ionic liquid were determined in temperature range of 293.2-343.2 K. The densities predicted by Gardas and Coutinho model showed good agreement with the experimental data obtained in this work. The critical temperature of [THTDP][Br] was estimated using the Eotvos correlation. Moreover, these experimental and calculated data gave an opportunity to apply the Peng-Robinson equation of state (PR-EoS) in order to predict/correlate the behaviour of the studied system, ([THTDP][Br] + CO2) with satisfactory results. (C) 2012 Published by Elsevier B.V.