Ionic liquids (ILs) have been proposed as potential inhibitors for preventing gas hydrate formation because their ion pairs effectively interrupt the hydrogen bonding between water molecules. ILs also have broad inhibitory capabilities depending on the specific cation and anion combinations. The final structural design of ILs for hydrate inhibition must be performed after an inhibition mechanism is suggested. In this study, the inhibitory thermodynamic effects of ILs were measured by the hydrateaqueous liquid-liquid carbon dioxide (CO2) equilibrium, and the experimental results were analyzed based on the hydration free energy of ILs calculated through molecular dynamics study. 1-Hydroxyethyl-1-methylpyrrolidinum chloride showed the best inhibitory performance of the suggested candidates. The anions mostly contributed to the thermodynamic inhibition, but the cations had a marginal impact on CO2 hydrate inhibition. Through fundamental understanding of the inhibition mechanism by both experimental and computational approaches, it is highly possible to provide crucial information for effective ILs to be designed as the CO2 hydrate inhibitor. (C) 2014 Elsevier B.V. All rights reserved.