The dissociation conditions for methane hydrates in the presence of (0.1 to 0.5) mass fraction 2-methy1-2-propanol aqueous solutions were experimentally measured in this study. The liquid water-hydrate-vapor (Lw-H-V) three-phase dissociation temperatures and pressures were determined using the isochoric method. New experimental data were reported within the pressure range from (4 to 10) MPa. It is demonstrated that the addition of 2-methyl-2-propanol had a promotion effect on the formation of methane hydrate. The liquid-hydrate-vapor (L-H-V) three-phase dissociation conditions for brine systems with methane + 0.035 mass fraction NaCl aqueous solution were also measured in this study with the addition of 2-methyl-2-propanol. The promotion effect for methane hydrate formation in brine environments was also observed with a 2-methy1-2-propanol additive.