Semi-clathrates were formed in an isochoric equilibrium-cell, from gaseous mixtures of (CO2 + H-2 + CO), in aqueous solutions of tetra-butyl ammonium bromide (TBAB). The experimental temperatures ranged between (282 and 291) K, experimental pressures ranged between (2.6 and 6.6) MPa and the experiments were conducted in aqueous TBAB solutions of w(TBAB) = (0.05, 0.10, and 0.20). The gas phase composition was analysed, using gas chromatography, and it was observed that the amount of CO2 in the gas phase was reduced. Additionally, the experimental results were compared to the formation conditions required for gas hydrates, that are formed from the same gas mixtures, and it was observed that the pressure required for semi-clathrate formation was significantly less than that required for gas hydrate formation. (C) 2012 Elsevier Ltd. All rights reserved.