In 1956, though, a geologist working for the Shell oil company published a report which showed, among other things, that the process of discovering, drilling and extracting an oil deposit took approximately four decades. It followed that if we calculate the point at which the maximum quantity of oil within a country is discovered, then we can expect that its rate of extraction will begin to decline four decades later. This, he argued, was a particular problem for the USA, whose peak of oil discovery was in 1930. This suggested that the USA's production peak would be reached sometime around 1970.