CO2 gas hydrate formation was clearly observed through Raman spectroscopy, when CO2 interacted with ice under high pressures of 1.6 MPa. The CO2 hydrate formation rate, which was measured by the change of the CO2 gas volume consumed by the CO2 hydrate formation, was found to be remarkably dependent on the temperature, especially at around the melting point of ice. At -10%, the CO2 hydrate formed gradually at reaction times longer than 1000 min. On the other hand, at -1 degreesC (just below the melting point of ice), the CO2 hydrate formed rapidly until 70 min, and the formation yield for the CO2 hydrate becomes close to the stoichiometric value estimated through the number of water molecules. These results suggest the mechanisms for CO2 gas hydrate formation depending on the temperature. At lower temperatures, the hydrate should be gradually growing only from the ice surface, because the delocalization of hydrate is hard to occur. On the other hand, at higher temperatures just below the melting point of ice, the delocalization of the hydrate in the ice is easy to occur, which generates the active surface for forming CO2 hydrates and keeps the reaction rate high. (C) 2002 Elsevier Science B.V. All rights reserved.