Petroleum: Reserves and Resources
As of January 1, 2007, ‘‘proved’’ world oil reserves were estimated at 1,208 billion barrels. Proved reserves are estimates of the amount of oil recoverable from known reservoirs under current economic and operating conditions. Proved reserves reflect only a fraction of the oil that a reservoir may hold. ‘‘Recoverable’’ oil includes proved reserves and undiscovered oil that is economically extractable.
Reserves are concentrated in theMiddle East and North Africa (MENA), together accounting for 62 percent of the world total. Saudi Arabia, with the largest reserves of any country, holds about a fifth of the world’s total reserves. Of the twenty countries with the largest reserves, seven are in the MENA region. Iranian oil reserves have increased by 46.6 billion barrels, or 52 percent, since 2000. Kazakhstan has had the third-largest increase, 24.6 billion barrels, since 2000. Among the top 20 reserve holders in 2007,11areOPECmember countries that, together, account for 65 percent of the world’s total reserves.
The United States Geological Survey (USGS) mean estimate of ultimately recoverable global conventional oil plus natural gas liquids (NGL) was 3.345 trillion barrels at the beginning of 1996. The estimates range from 2.5 to 4.4 trillion barrels, expressed in statistical terms, where 2.5 trillion barrels represents a 95 percent probability that the quantity size will exceed the estimate, and 4.4 trillion barrels indicates a 5 percent probability that the quantity will exceed the estimate. By comparison, IOCs project an average of 3.5 trillion barrels. The IOC most-likely estimates for ultimately recoverable global conventional oil range from 2.8 to 4.0 trillion barrels.
The uncertainty of ultimate recoverable oil and NGL has led to a continuing debate about the prospect of a future oil production peak and eventual decline.The timing of a peak and subsequent decline is subject to interpretation because of a number of variables, such as lack of transparent reporting of producing fields, conflicting estimates of recoverable oil, the increased costs of producing oil from conventional and nonconventional sources, and the timing and scale of development of alternative fuels.