Natural gas is a combustible energy source produced from underground gas deposits. Due to its similar origin, natural gas is often found together with crude oil. Natural gas mainly consists of methane. It comes in two quality levels that depend on its exact methane content and the region in which it is produced: H-gas and L-gas. H-gas has the highest quality due to its high methane content (between 87 % and 99 %). L-gas is natural gas with a lower methane content of between 80 % and 87 %.