Abstract The dynamics of CH 4 replacement in CH 4 hydrate with high-pressure CO 2 was observed with in situ laser Raman spectroscopy at temperatures ranging from 271.2 to 275.2 K and at an initial pressure of 3.25 MPa. The amount of CH 4 hydrate decomposition was found to be almost proportional to that of CO 2 hydrate formation for a series of 150 h experiments at fixed temperatures. This confirmed that the CH 4 –CO 2 replacement mainly occurred in the hydrate phase. Based on the rate data, a kinetic model was developed for CH 4 hydrate decomposition and CO 2 hydrate formation. Under CH 4 –CO 2 replacement in the hydrate, the activation energies were determined to be 14.5 kJ/mol for CH 4 hydrate decomposition and 73.3 kJ/mol for CO 2 hydrate formation after a given initial period (ca. 10 h). It was found that CH 4 hydrate decomposition was probably dominated by re-arrangement of water molecules in the hydrate whereas CO 2 hydrate formation seemed to be dominated by diffusion in the hydrate phase.