Is the world running out of oil? Where will future oil and gas supplies come from? To help answer these questions, in 2000 the U.S. Geological Survey completed a new world assessment, exclusive of the United States, of the undiscovered conventional oil and gas resources and potential additions to reserves from field growth.² One hundred and twenty-eight provinces were assessed in a 100 manyear effort from 1995-2000. The assessed provinces included 76 priority provinces containing 95% of the world's discovered oil and gas and an additional 52 "boutique" provinces, many of which may be highly prospective. Total Petroleum Systems (TPS) were identified and described for each of these provinces along with associated Assessment Units (AU) that are the basic units for assessing undiscovered petroleum. The assessment process coupled geologic analysis with a probabilistic methodology to estimate remaining potential. Within the 128 assessed provinces were 159 TPS and 274 AU. For these provinces, the endowment of recoverable oil—which includes cumulative production, remaining reserves, reserve growth, and undiscovered resources—is estimated at about 3 trillion barrels of oil (TBO). The natural gas endowment is estimated at 2.6 trillion barrels of oil equivalent (TBOE). Oil reserves are currently 1.1 TBO; world consumption is about .028 TBO per year. Natural gas reserves are about 0.8 TBOE; world consumption is about 0.014 TBOE per year. Thus, without any additional discoveries of oil, gas or natural gas liquids, we have about 2 TBOE of proved petroleum reserves. Of the oil and gas endowment of about 5.6 TBOE, we estimate that the world has consumed about 1 TBOE, or 18%, leaving about 82% of the endowment to be utilized or found. Half of the world's undiscovered potential is offshore. Arctic basins with about 25% of undiscovered petroleum resources make up the next great frontier. An additional 279 provinces contain some oil and gas and, if considered, would increase the oil and gas endowment estimates. Whereas petroleum resources in the world appear to be significant, certain countries such as the United States may run into import deficits, particularly oil imports from Mexico and natural gas from both Canada and Mexico.

The new assessment has been used as the reference supply case in energy supply models by the International Energy Agency and the Energy Information Agency of the Department of Energy. Climate energy modeling groups such as those at Stanford University, Massachusetts Institute of Technology, and others have also used USGS estimates in global climate models. Many of these models using the USGS estimates converge on potential oil shortfalls in 2036-2040. However, recent articles using the USGS (2000) estimates suggest peaking of oil in 2020-2035 and peaking of non-OPEC (Organization of Petroleum-Exporting Countries) oil in 2015-2020. Such a short time framework places greater emphasis on a transition to increased use of natural gas; i.e., a methane economy. Natural gas in turn may experience similar supply concerns in the 2050-2060 time frame according to some authors.

Coal resources are considerable and provide significant petroleum potential either by extracting natural gas from them, by directly converting them into petroleum products, or by utilizing them to generate electricity, thereby reducing natural gas and oil requirements by fuel substitution. Non-conventional oil and gas are quite common in petroleum provinces of the world and represent a significant resource yet to be fully studied and developed. Seventeen non-conventional AU including coal-bed methane, basin-center gas, continuous oil, and gas hydrate occurrences have been preliminarily identified for future assessment. Initial efforts to assess heavy oil deposits and other non-conventional oil and gas deposits also are under way.