Natural gas hydrates are solid compounds with cage-like structures formed by gas and water. An intriguing phenomenon that gas hydrates can dissociate at a low rate below the ice freezing point has been viewed as the metastability of hydrate. The mechanisms of hydrate metastability have been widely studied

and many mechanisms were proposed involving the self-preservation effect

supercooled water-gas-hydrate metastable equilibrium

and supersaturated liquid-gas-hydrate system etc. The metastable state of hydrate could be of crucial significance in the kinetics of hydrate formation and decomposition

heat and mass transfer during gas production processes

and the application of hydrate-based technique involving desalination

energy storage and transportation

and gas separation and sequestration. Few researches have systematically considered this phenomenon

and its mechanism remains unclear. In this work

various mechanisms and hypothesis explaining the metastable state of gas hydrates were introduced and discussed. Further studies are still required to reveal the intrinsic nature of this metastable state of gas hydrate

and this work could give some implications on the existing theory and current status of relevant efforts.