The Hubbert curve is an approximation of the production rate of a resource over time. It is a symmetric logistic distribution curve,[1] often confused with the "normal" gaussian function. It first appeared in "Nuclear Energy and the Fossil Fuels," geologist M. King Hubbert's 1956 presentation to the American Petroleum Institute, as an idealized symmetric curve, during his tenure at the Shell Oil Company.[1] It has gained a high degree of popularity in the scientific community for predicting the depletion of various natural resources. [dubious – discuss] [citation needed] The curve is the main component of Hubbert peak theory, which has led to the rise of peak oil concerns. Basing his calculations on the peak of oil well discovery in 1948, Hubbert used his model in 1956 to create a curve which predicted that oil production in the contiguous United States would peak around 1970.[1]