Methane Hydrates [Photo courtesy Ian MacDonald]

What they are: Under conditions of high pressure and low temperatures, methane, a gas, combines with water to form a solid, ice-like substance. Early during the Deepwater Horizon oil spill, BP attempted to place a containment dome over the broken well and pump out the oil and gas to ships on the surface. Methane hydrates formed inside the structure and clogged the outflow of oil and gas, however.

Where they are: Worldwide. On or just below the seafloor in water more than 500 meters deep, along the coastal regions of most continents, particularly in areas where there are oil and gas deposits deeper in the ground. Also in permafrost regions in Alaska, Canada and Russia.

U.S. annual consumption of natural gas: 23 trillion cubic feet

Resource potential of methane hydrates: In the U.S. alone, 200,000 trillion cubic feet

The challenge: Freeing the methane from the hydrate economically and safely for use as a fuel