Editing Hubbert peak theory (section)

====Crude oil====
[[File:Hubbert Upper-Bound Peak 1956.png|thumb|Hubbert's upper-bound prediction for US crude oil production (1956), and actual lower-48 states production through 2016]]
Hubbert, in his 1956 paper,<ref name="Hubbert1956"/> presented two scenarios for US crude oil production:
* most likely estimate: a logistic curve with a logistic growth rate equal to 6%, an ultimate resource equal to 150 Giga-barrels (Gb) and a peak in 1965. The size of the ultimate resource was taken from a synthesis of estimates by well-known oil geologists and the US Geological Survey, which Hubbert judged to be the most likely case.
* upper-bound estimate: a logistic curve with a logistic growth rate equal to 6% and ultimate resource equal to 200 Giga-barrels and a peak in 1970.
Hubbert's upper-bound estimate, which he regarded as optimistic, accurately predicted that US oil production would peak in 1970, although the actual peak was 17% higher than Hubbert's curve. Production declined, as Hubbert had predicted, and stayed within 10 percent of Hubbert's predicted value from 1974 through 1994; since then, actual production has been significantly greater than the Hubbert curve. The development of new technologies has provided access to large quantities of unconventional resources, and the boost of production has largely discounted Hubbert's prediction.{{Citation needed|date=October 2018}}

Hubbert's 1956 production curves depended on geological estimates of ultimate recoverable oil resources, but he was dissatisfied by the uncertainty this introduced, given the various estimates ranging from 110 billion to 590 billion barrels for the US. Starting in his 1962 publication, he made his calculations, including that of ultimate recovery, based only on mathematical analysis of production rates, proved reserves, and new discoveries, independent of any geological estimates of future discoveries. He concluded that the ultimate recoverable oil resource of the contiguous 48 states was 170 billion barrels, with a production peak in 1966 or 1967. He considered that because his model incorporated past technical advances, that any future advances would occur at the same rate, and were also incorporated.<ref>M. King Hubbert, 1962, "Energy Resources," National Academy of Sciences, Publication 1000-D, p. 60.</ref> Hubbert continued to defend his calculation of 170 billion barrels in his publications of 1965 and 1967, although by 1967 he had moved the peak forward slightly, to 1968 or 1969.<ref>{{cite journal |last1=Hubbert |first1=M. King |title=National Academy of Sciences Report on Energy Resources: REPLY |journal=AAPG Bulletin |date=1 October 1965 |volume=49 |issue=10 |pages=1720–1727 |doi=10.1306/A66337C0-16C0-11D7-8645000102C1865D }}</ref><ref>{{cite journal |last1=Hubbert |first1=M. King |title=Degree of Advancement of Petroleum Exploration in United States |journal=AAPG Bulletin |date=1 November 1967 |volume=51 |issue=11 |pages=2207–2227 |doi=10.1306/5D25C269-16C1-11D7-8645000102C1865D }}</ref>

A post-hoc analysis of peaked oil wells, fields, regions and nations found that Hubbert's model was the "most widely useful" (providing the best fit to the data), though many areas studied had a sharper "peak" than predicted.<ref name=Brandt2007>{{cite journal |last1=Brandt |first1=Adam R. |title=Testing Hubbert |journal=Energy Policy |date=May 2007 |volume=35 |issue=5 |pages=3074–3088 |doi=10.1016/j.enpol.2006.11.004 |bibcode=2007EnPol..35.3074B }}</ref>

A 2007 study of oil depletion by the [[UK Energy Research Centre]] pointed out that there is no theoretical and no robust practical reason to assume that oil production will follow a logistic curve. Neither is there any reason to assume that the peak will occur when half the ultimate recoverable resource has been produced; and in fact, empirical evidence appears to contradict this idea. An analysis of a 55 post-peak countries found that the average peak was at 25 percent of the ultimate recovery.<ref>Steve Sorrell and others, ''Global Oil Depletion'', UK Energy Research Centre, {{ISBN|1-903144-03-5}}.{{page needed|date=January 2021}}</ref>