The U.S. Geological Survey (USGS) periodically conducts geology-based assessments of the oil and gas resources of the world in recognition of the fact that the United States economic security is closely linked to energy resources outside the United States. Four such petroleum assessments have been published in recent years (Masters and others, 1984, 1987, 1991, and 1994). A summary of these assessments (table 1) indicates the magnitude of world conventional oil and gas resources, as perceived in the 1980s and 1990s by the USGS.
These four successive world petroleum assessments evidence changes in perception through time. The assessments were prepared using a consistent methodology by the same core group of geologists. Because of this continuity, differences among the four assessments can be largely attributed to an evolving understanding of world recoverable oil and gas resources rather than to procedural or philosophical changes. In this fact sheet, some of the trends in the estimates of table 1 are examined with a view toward better understanding world oil and gas resources in the context of the next few decades.
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