Controlled decomposition experiments conducted on pure methane hydrate show that dissociation kinetics and phase stability are strongly dependent on the specific pressure-temperature-time (P-T-t) history of the material. Flow rates and amounts of methane (CH4) gas released during hydrate dissociation to H2O CH4 were measured over the temperature range 190 to 290 K at 0.1 MPa on samples of polycrystalline methane hydrate. Samples were removed from initially stable conditions of low temperature or elevated pressure by either slow warming of cold material to temperatures above equilibrium conditions of 193 K at 0.1 MPa, or by rapid depressurization from elevated methane pressure to 0.1 MPa. Those samples dissociated by slow warming decomposed readily in bulk to H2O ice CH4 gas by 205 K, with an additional amount (3- 5%) of CH4 released as temperatures approached 273 K. When destabilized by rapid depressurization to 0.1 MPa at external isothermal conditions of 195<T20) hours as dissociation rates slowed markedly after an initial degassing pulse. Upon subsequent warming through 273 K, up to 93% of the expected gas yield was recovered from several of these anomalously preserved samples. Anomalous preservation was particularly pronounced at the warmer test temperatures of 268- 270 K, and may be caused in part by healing of crack networks and by enhanced mobility and annealing of grain boundaries near the ice melting temperature, effects that close off gas migration pathways necessary for sustained and rapid decomposition. Curiously, metastable hydrate made by this technique can be cooled from 270 to 193 K without further decomposition, but upon slow rewarming above 193 K, it readily dissociates near 205 K.