In the 1970s, geologists discovered crystalline natural gas—methane hydrate, in the jargon—beneath the seafloor. Stored mostly in broad, shallow layers on continental margins, methane hydrate exists in immense quantities; by some estimates, it is twice as abundant as all other fossil fuels combined. Despite its plenitude, gas hydrate was long subject to petroleum-industry skepticism. These deposits—water molecules laced into frigid cages that trap “guest molecules” of natural gas—are strikingly unlike conventional energy reserves. Ice you can set on fire! Who could take it seriously? But as petroleum prices soared, undersea-drilling technology improved, and geological surveys accumulated, interest rose around the world. The U.S. Department of Energy has been funding a methane-hydrate research program since 1982.