The Hubbert peak theory says that for any given geographical area, from an individual oil-producing region to the planet as a whole, the rate of petroleum production tends to follow a bell-shaped curve. It is one of the primary theories on peak oil. Choosing a particular curve determines a point of maximum production based on discovery rates, production rates and cumulative production. Early in the curve (pre-peak), the production rate increases due to the discovery rate and the addition of infrastructure. Late in the curve (post-peak), production declines because of resource depletion. The Hubbert peak theory is based on the observation that the amount of oil under the ground in any region is finite, therefore the rate of discovery which initially increases quickly must reach a maximum and decline. In the US, oil extraction followed the discovery curve after a time lag of 32 to 35 years. The theory is named after American geophysicist M. King Hubbert, who created a method of modeling the production curve given an assumed ultimate recovery volume. "Hubbert's peak" can refer to the peaking of production of a particular area, which has now been observed for many fields and regions. Hubbert's peak was thought to have been achieved in the United States contiguous 48 states (that is, excluding Alaska and Hawaii) in the early 1970s. Oil production peaked at per day in 1970 and then declined over the subsequent 35 years in a pattern which closely followed the one predicated by Hubbert in the mid-1950s. However, beginning in the mid-2000 decade, advances in extraction technology, particularly those that led to the extraction of tight oil and unconventional oil resulted in a large increase in U.S. oil production, thus establishing a pattern which deviated drastically from the model predicted by Hubbert for the contiguous 48-states as a whole. In November 2017 the United States once again surpassed the 10 million barrel mark for the first time since 1970.