According to Hubbert peak theory, peak oil is the date when the peak of the world's production of conventional petroleum (crude oil) is reached. After this date the rate of production is forecast to enter terminal decline, following the bell-shaped curve predicted by the theory. Due to the world's high dependence on inexpensive oil, it is thought that severe price increases may result, with serious implications for the global economy.
Acceptance of peak oil is far from universal, and the only reliable way to identify its existence will be in retrospect. One alternative scenario is that global production will eventually follow an 'undulating plateau' for one or more decades before declining slowly.
Having accurately predicted the date of peak production in the US petroleum industry, which occurred in 1970, M. King Hubbert, who devised the theory, forecast that the world peak would occur in 1995 'if current trends continue'. Various subsequent predictions have been made as trends have fluctuated in the intervening years. Two milestones have passed, however. The peak of world oilfield discoveries occurred in 1965 and, due world population growth, production per capita peaked in 1979.
The effects of peak oil could be mitigated through conservation and switching to alternative fuels or unconventional oil sources. Such changes would bring their own challenges, ranging from the need to development alternative technologies to potential increases in greenhouse gas emissions.