Experiments at 8.0 MPa and 277.15 K were carried out in different porous media, such as silica sand and activated carbon, to observe the formation and dissociation of methane hydrate in a specially designed crystallizer for mophology observation. In silica sand bed, we observed a clear hydrate front moving across the bed in the crystallizer at the experimental conditions with 50 and 100% water saturation. The hydrate crystals were observed to form in the interstitial pore space available between the silica sand particles. Whereas in activated carbon bed experiments, hydrates were observed to nucleate on the surface of the activated carbon grain and then dissociate within the stable hydrate formation region. For the first time, we were able to observe this behavior of transient hydrate crystal formation/dissociation in the stable hydrate region in porous media. We postulated that the particle size, pore space, and water saturation level may play a role in the above phenomenon. A clear hydrate front movemen...