World Oil and Gas Resources: How Much is Left? Where is It? How Do We Find It?

Peter J. McCabe
Petroleum Resources Division, CSIRO, North Ryde, NSW, Australia ([email protected])

Reported reserves (discovered) and estimated resources (discovered and undiscovered) identify only a fraction of the global abundance of oil based on selected criteria and subjective classification. For example, in 2000 the U.S. Geological Survey (USGS) estimated the original recoverable resource base to be approximately 3 trillion barrels of oil. By the end of 2006, 1 trillion barrels had been produced and it would be easy to conclude that one-third of the World’s oil has been produced. However, it is only correct to say that one-third of the USGS-assessed oil has been produced. There is a large volume over and above this amount, including small oil fields, oil in unexplored or under-explored frontier basins (in regions such as the Arctic, the Indian Ocean, and offshore Australasia), oil that may be recovered from reservoirs with the application of new technologies (reserve growth) after the year 2025, and oil that may be extracted from oil sands and oil shales. Most of this additional volume of oil was not assessed by the USGS because it cannot be produced economically using current technologies. History, however, shows that resources regarded as inaccessible or uneconomic can eventually be produced as technological advances reduce costs. The ultimate amount of oil produced could, therefore, far exceed 3 trillion barrels.
An understanding of the global geographic distribution of oil is critical to consideration of future energy scenarios. Like other geologic-based commodities, oil is widespread but is enriched in a small number of locations where the geologic history has been particularly favorable for accumulation and preservation. Although oil is produced in more than 110 countries, over 50% of the remaining economic oil lies within just five countries: Saudi Arabia, Russia, United States., Iran, and Iraq. This geographic concentration has profound geopolitical implications, especially if there is instability within a major producing country or disruption in the supply routes. In this regard, it is worth noting that much of the oil that was not assessed by the USGS may have a distinctly different geographic distribution. The majority of the world’s oil sands and oil shales, for example, lie within North America. Technological advances could make much of these resources economically viable. Already oil from Alberta’s oil sands accounts for 39% of Canada’s oil production and is forecast to quadruple by 2020.

AAPG Search and Discovery Article #90073 © 2007 AAPG Foundation Distinguished Lecturer Series 2007-2008