Something like 700 milliard cubic yards of gas a year are produced by gas wells in various parts of the world. Most of this is combustible gas now generally referred to as natural gas.

Some natural gas wells also produce incombustible or highly toxic gases such as carbon dioxide, sulphur dioxide, hydrogen sulphide and others, in rare cases also inert gases such as helium neon and argon. The sulphurous gases for the most part are of volcanic origin and are formed deep down in the earth's crust. Natural gas in the more specific sense of combustible hydrogen is usually found in regions where petroleum is also likely to occur.

Many gas wells produce so called wet natural gas containing petrol vapor which can be separated and utilized. For example, in the United States, up to 10% of the country's petrol consumption is supplied from this source. In dry natural gas, in addition to methane a small quantity of the following gases are often found to be present: carbon monoxide, hydrogen, helium, neon, argon, and nitrogen.

Natural gas provides a very significant part of the raw material for energy production: in terms of energy content the annual output of natural gas corresponds to 350 million tons of coal. A large proportion of the natural gas is conveyed through huge pipelines from the wells to the industrial centers and major cities, where it is used for industrial and domestic heating. A proportion is also used as fuel for gas engines which drive electricity generating plant. Also, an increasing proportion of the natural gas output is chemically processed into motor fuels, plastics, man-made fibers, synthetic rubber, anti-freeze preparations, alcohols, solvents, insecticides etc.

Besides the naturally existing gas wells, increasing numbers of artificial wells drilled for tapping the underground gas supplies. Some of these wells deliver gas pressures of 2000 lb/in2 and upwards. Sometimes former gas-fields are used as underground storage reservoirs - sometimes of 1½ milliard cubic yards capacity -for natural gas which may first have been chemically cleaned and had their petrol content removed.

Large quantities of natural gas are found at the foot of the western Pyrenees. In recent years, too, very large supplies of natural gas have been discovered in Holland.