What keeps oil and natural gas from escaping to the surface of the Earth?
Oil and natural gas are often found under rock formations called “caprock” that are dense enough to trap the oil and gas and keep it from seeping to the surface. Some oil and natural gas have been found at the surface of the Earth. Marco Polo, an Italian explorer, wrote of seepages of oil in the Caspian Sea region. The “eternal fires” reported by Plutarich, a Greek historian, in the area of present day Iraq probably were natural gas seepages that had been ignited by lightning.
