In the 40 years since surface geochemical prospecting was first developed, extensive studies have been made by major oil company research laboratories, academic institutions and geochemical service companies both in the United States and abroad. Despite this wealth of data, there are still conflicting opinions as to the value of surface prospecting in finding oil and gas.

There is ample evidence that many petroleum accumulations leak hydrocarbons to the surface via faults, fractures, unconformities, intrusions, and highly permeable sediments. Migration can occur in a wide range of concentrations from the visible to the invisible, as a discrete hydrocarbon phase or in solution. These migration mechanisms follow erratic pathways upward causing surface anomalies that may have prospecting value when combined with conventional geological and geophysical exploration methods plus an understanding of the ground-water flow regime. Upward migration is most likely in tectonically active areas, and least likely in quiet areas, especially where there are widespread barriers to migration such as evaporites.

The interpretations of these anomalies are best used in a regional sense since there is no known mechanism that will cause a subsurface pool to be outlined at the surface. Furthermore, the mixing of upward migrating hydrocarbons with near-surface generated hydrocarbons confuses the detailed local interpretations. Even regional evaluations can be risky since some areas with valid surface shows are studded with dry holes. Nevertheless, when no subsurface cuttings are available, surface prospecting can indicate, under favorable conditions, if an area is alive or dead with respect to hydrocarbons.

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