Natural methane hydrate deposits offer a potentially vast source of energy, greatly surpassing all known fossil fuel resources, but many questions and challenges remain before these deposits can be tapped. Clathrate hydrates, which consist of a gas molecule surrounded by a cage of water molecules to form an ice-like structure, could in theory also be used to sequester carbon dioxide at the bottom of the ocean. Gas hydrates form at low temperatures and ocean depths of about 500 meters and some scientists see them as an energy source that could provide a transition to a hydrogen-based economy. Of more immediate concern is the hazard these deposits pose to gas and oil drilling operations in deep marine and onshore Arctic settings. Gas kicks, blowouts and fires result when workers penetrate pockets of gas hydrates. Another concern is the effect discharge of methane might have on global warming. A special 17-paper August/September issue of American Mineralogist, edited by Bryan Chakoumakos of Oak Ridge National Laboratory, offers an in-depth exploration of clathrate hydrates.