The only known natural gas fields in the world that yield gas sufficiently rich in helium to warrant the extraction of the element on a commercial scale occur in the United States. Rich helium and nitrogen gas occurs in several fields in southeastern Kansas, in Vinton and Meigs counties, Ohio, in southeastern Colorado, in the Texas Panhandle, and eastern Utah. The percentage of helium in the richest gases ranges between 1.0 and 8.0 per cent. The age of the helium gas-producing formations ranges from Cambrian to Tertiary. In Canada, gas containing as much as 1.0 per cent of helium has been found in Ontario, but the supply of gas is too small and the rock pressures are too low for commercial helium processing. Elsewhere in the world, so far as known, natural gases are poor n helium. The occurrence of many of the rich helium gases in reservoirs lying close to the crystalline rocks strengthens the theory that the helium in some natural gases, at least, has been derived from the disintegration of the radioactive elements in the basement rocks.

Deep wells yielding natural gas rich in carbon dioxide are confined chiefly to the western part of the United States and to the Panuco district, Mexico. The gas occurs in rocks ranging in age from Cambrian to Tertiary and probably originated from the metamorphism of basement rocks lying at relatively shallow depth, the oxidation of hydrocarbons through contact with mineralized waters, and the reaction of hot magmas on limestone.

Natural gas rich in hydrogen sulphide is produced chiefly from limestone in many areas, especially in the Permian fields of western Texas.