The gas capacity of the present HS-I hydrate was confirmed by gas uptake tests and phase 20 equilibrium measurements. The D cage occupancy (or conversion) data for the present HS-I hydrate obtained from the bulk phases were given in Fig. and Table in Supporting Information. In comparison with the CS-II hydrate, the present HS-I hydrate showed better occupancy for CO2 gas, while it had the slightly lower occupancy for CH4 gas. The orthorhombic Pmma hydrate of TBA bromide (TBAB), which is a widely used ionic guest, clearly showed the lowest gas capacity likely due to its low symmetric structure. The three phase (gas-hydrateliquid) equilibrium data also supported the higher gas capacity of N4446Cl hydrates than those of TBAB (see Supporting Information). Another important finding is that the equilibrium temperatures for the N4446Cl + CO2 hydrates are higher than those with CH4. Since the molecular size of CO2 is slightly large for the D cage, the conventional promoted clathrate hydrates, showed irregular capture properties of CO2 such as the inconsistent cage occupancies in CS-II hydrates and the scarce HS-III hydrate formation under CO2 pressure .