For many years geologists and chemists have been aware of the presence of certain significant density patterns developed by analyzing surface soils over oil and gas reservoirs. Geochemists have

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made use of this method in studying oil and gas prospects, in addition to structural geology and geophysics.

By use of organic geochemistry there was later developed a new method of semi-direct surveying based on the development of density patterns in the surface soil by analysis for certain inorganic substances. It naturally followed that any radioactive inorganic elements contained in the surface soil would allow the development of a similar concentration pattern which could be mapped by the use of highly sensitive radiation counters.

Serious radiation surveys were begun about ten years ago with the use of an ionization-type instrument of suitable sensitivity and stability. These instruments were built to order and required a considerable period of testing and improvement to prove their reliability.

With the new interest in uranium exploration stimulated by the building of highly sensitive scintillometer devices, these instruments have also become available for oil exploration.

The successful use of all types of sensitive radiation-measuring instruments depends on the proper handling of numerous factors that tend to create false radiation values. Obviously this method, like geochemistry, is not simple. It is the purpose of this paper to attempt to describe and evaluate all factors which must be taken into consideration before a survey can be completed and the correct conclusions reached.

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