Oil resources for the next century: What's ahead?

Proven reserves of liquid hydrocarbons are now assessed at between 950 and 1,000 billion barrels, depending on the source. Their life expectancy at the current rate of world production is about 41 to 45 years. This lifetime is much longer than what was predicted in both 1970 and 1980. However, this wealth of resources does not necessarily mean that the security of oil supplies is guaranteed for all countries. Oil reserves are unequally distributed from a geopolitical standpoint. Reserves and output are mainly due to big fields (with more than 500 million barrels of initial reserves).Though oil supplies seem to be ensured for the coming 30 to 40 years, what does the picture look like beyond 2020–20307 The increased lifetime of proven oil reserves has been apparent only in the last 10 to 20 years. The considerable increase in proven oil reserves reported after 1986 is, in fact, mainly due to revisions and extensions, rather than to new sources of oil: conventional oil (with the price per barrel of oil on the order of $20 and recovery rate around 30 percent) remaining to be discovered today; oil resources stemming from an improvement in recovery rate; oil resources resulting from exploitation of new zones, such as deep sea zones; and unconventional types of oil, such as extra-heavy crudes, tar sands, shale oils, and liquid hydrocarbons from chemical-enhanced oil recovery methods.