• The world has produced about 1 trillion barrels of oil since the start of the industry in the nineteenth century. Currently, it is thought that there are at least 5 trillion barrels of petroleum resources, of which 1.4 trillion is sufficiently developed and technically and economically accessible.

    Daniel Yergin (2011). “The Quest: Energy, Security, and the Remaking of the Modern World”, p.207, Penguin