Experimental data on the kinetics of formation of structure H gas hydrate obtained in a semibatch stirred vessel at pressures of 0.63-1.5 MPa above equilibrium are reported. Methane was used as a guest substance and neohexane, tent-butyl methyl ether, and methylcyclohexane were used as the large molecule guest substance (LMGS). The results indicate that the rates of hydrate formation and the induction times are dependent on the magnitude of the driving force and the type of LMGS. When tent-butyl methyl ether is used as the LMGS, rapid hydrate formation and a much smaller induction time can be achieved. Furthermore, the methane consumption rate for hydrate formation in the presence of tent-butyl methyl ether is 3 times greater than that for a pure methane-water system. It was also observed that, although the induction period was greatly shortened by the memory effect, the rate of gas consumption rate was not affected. Hydrate decompositions were also conducted at a pressure 20% below equilibrium. The system with tertbutyl methyl ether as LMGS exhibited the fastest decomposition rate.