Gas well. View of the Sun setting behind the drilling tower at an onshore gas well. Gas is a fossil fuel which occurs as a result of the breakdown of organic matter. It occurs mainly at the top of oil wells, although it may exist in wells of its own. It consists largely of the gases methane and ethane. Heavier gases, such as butane, are generally removed before the gas is used as fuel. The drilling tower here contains a powerful drill which digs through the earth and rock to reach the reservoir of gas. Pipes (some seen standing vertically to the right of the tower) are passed down with the drill to collect the gas. Photographed in Lincolnshire, England.