In the 1950s, a petroleum geologist named M. King Hubbert published a series of equations showing that the output of any given oil well or reservoir will follow a parabolic curve over time, with production rising quickly after initial drilling and then losing momentum as output reaches its peak, after which production will fall at an increasingly sharp rate. Using these equations, Hubbert predicted in 1956 that conventional (i.e., liquid) oil output in the United States would peak in the early 1970s—a prediction that provoked much derision at the time but later earned him considerable renown when US oil production was realized to have achieved a record level of 11.6 million barrels per day in 1972, after which it began its long decline. Hubbert was unable to apply his equations to non-US production because of insufficient data, but he did predict that global output would also reach a summit and then begin to fall.

Today the concept of global peak oil is widely accepted in the energy field. The debate is over when this moment will occur. Those who wish to believe that oil supplies are abundant tend to put this date far in the future. The Department of Energy predicted in its International Energy Outlook for 2004 that conventional oil will “peak closer to the middle than to the beginning of the 21st century.” But analysts who don’t work for the current administration are not so sanguine. “The peak will occur in late 2005 or in the first few months of 2006,” writes Princeton geologist Kenneth S. Deffeyes in a new book, Beyond Oil. A more conservative estimate, by Mike Rodgers of PFC Energy, puts the peak at 2010 or 2015. If either of these estimates proves accurate, the global oil supply will never climb high enough to satisfy the elevated consumption levels projected by the DOE for 2025 and beyond.

Whether peak oil arrives in 2005 or 2010 or 2015, and whether the maximum level of production turns out to be 90 or 100 million barrels per day, will not matter much in the end. All economies run on energy, and since World War II the most important source of that energy has been petroleum. From 1950 until the present, global petroleum consumption grew from approximately 10 millon to 80 million barrels a day, and as the rest of the world accelerates into industrialization, the next twenty years will likely see a 50 percent rise in demand. No matter when peak oil arrives, global oil production will level off and decline to a rate far below the anticipated world demand of 120 million barrels per day in 2025. True, some of this shortfall may be absorbed by the intensified development of “unconventional” fuels—liquid condensate from the production of natural gas, fuels derived from tar sands and oil shale, liquids extracted from coal, and so on—but these materials are too costly to produce and their manufacture requires too many environmental risks for them to be considered practical substitutes for conventional oil. Tar-sand development, for example, entails the extravagant consumption of natural gas—itself a valuable (and finite) form of energy—to produce the steam needed to drive the oil-laden oars to the surface, and releases substantial climate-altering greenhouse gases in the process.

In any case, the contraction in global petroleum supplies can be postponed for only a few years. We are now in the Twilight Era of petroleum, marked by recurring shortages, frequent price hikes, and political instability. At some point in the not-too-distant future, Twilight will give way to Nightfall, when acute oil scarcity becomes a permanent fact of life. Cheap petroleum is the fundamental premise of globalization—of American dominance, the rise of China, and the harmonious coexistence of various national economies—and that premise cannot be sustained.