Michel T. Halbouty Distinguished Lecturer: World Fossil Fuel Resources: How Much Is Left? How Valid Are Predictions about Future Production?

Resource assessments for geologic commodities are not absolute measurements. They represent judgments of the amount of available resource within the foreseeable future. With advances in geologic knowledge, technological advancements, and changing commodity prices and production costs, it is necessary to periodically reassess resources. Assessments of conventional oil and natural gas have tended to increase the resource base. Assessments of coal and unconventional oil and gas resources have historically tended to overestimate the resource base either because of unrealistic economic considerations or because the geologic nature of the resource was poorly understood. History, shows that resources regarded as inaccessible or uneconomic may eventually be produced as technological advances reduce costs. Oil sands, shale gas, coal-bed methane, and deep-water oil are all resources that until recently were not viable sources for energy production.

Oil, gas and coal have consistently supplied between 91 and 93% of the world's energy supply for the last 60 years. Temporal variations in resource assessments and the economic uncertainties related to energy demand have always combined to make long-term prediction of actual fossil energy production difficult but, given the abundance of remaining fossil fuels, they are likely to remain the dominant part of the world's energy mix for decades to come.

An understanding of the global geographic distribution of fossil fuel is critical to consideration of future energy scenarios. Fossil fuels are widespread but enriched in a small number of locations where the geologic history was favorable for accumulation and preservation. Oil, for example, is produced in more than 110 countries but over 50% of the remaining economic oil lies within just five countries: Saudi Arabia, Russia, USA, Iran, and Iraq. Geographic concentration of energy resources has profound geopolitical implications, especially if there is instability within a major producing country or disruption in the supply routes.