The pictures went around the world. In April 2010, huge amounts of methane gas escaped from a well below the Deepwater Horizon platform in the Gulf of Mexico. This “blow-out” caused an explosion, in which eleven people died. For several weeks, oil spilled from the damaged well into the ocean. Fortunately, such catastrophic “blow-outs” are rather rare. Continuous discharges of smaller amounts of gas from active or old and abandoned wells occur more frequently.