As Richard Monastersky points out in Science News Online, no-one has yet been able to show that extracting natural gas out of gas hydrate deposits is commercially viable. While hydrates are abundant worldwide, scientists are unsure what percentage of deposits occur in commercially extractable concentrations. Most gas hydrate deposits sit far offshore in water depths of at least 600m. In this environment, low temperatures and extreme pressure combine to squeeze methane and water into a crystalline structure. Each molecule of methane gets trapped in a cage-like lattice of frozen water molecules an arrangement that concentrates a large amount of methane into a small space.
Hydrates also go by the name of clathrates, a term derived from the Latin word for lattice.
The methane in most hydrate deposits originally comes from bacteria living beneath the seafloor. As they consume plant and animal remains in the sediment, the bacteria excrete methane. In some deposits, the source of the gas comes from deeper sediments warmed by the Earth internal heat. Several kilometers below the seafloor, sediment temperature is so high that it cooks the buried organic debris. This produces petroleum and hydrocarbon gases that leak upward toward the seafloor.