Studies have been made by several laboratories on the isotopic and chemical abundances of He, Ne, Ar, Kr, and Xe in natural gases from both gas wells and geothermal areas. This work has shown that the rare gases consist of a mixture of two distinct components--atmospheric and radiogenic. These investigations give information on the evolution of natural gas accumulations from considering the dissolved atmospheric components and the production of He³⁴, A⁴⁰ and Xe from nuclear processes. The importance of solubility phenomena in fractionation of these elements may be approached by using a simple model. Measurements of

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the radiogenic gases permit estimates of the rate of evolution of the atmosphere.

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