Gas hydrates from CO2 / N2 and CO2 / H2 gas mixtures were formed in a semi-batch stirred vessel at constant pressure and temperature of 273.7 K. These mixtures are of interest to CO2 separation and recovery from flue gas and fuel gas, respectively. During hydrate formation the gas uptake was determined and the composition changes in the gas phase were obtained by gas chromatography. The rate of hydrate growth from CO2 / H2 mixtures was found to be the fastest. In both mixtures CO2 was found to be preferentially incorporated into the hydrate phase. The observed fractionation effect is desirable and provides the basis for CO2 capture from flue gas or fuel gas mixtures. The separation from fuel gas is also a source of H2. The impact of tetrahydrofuran (THF) on hydrate formation from the CO2 / N2 mixture was also observed. THF is known to substantially reduce the equilibrium formation conditions enabling hydrate formation at much lower pressures. THF was found to reduce the induction time and the rate of hydrate growth. © 2007 Elsevier Ltd. All rights reserved.