"It is commonly asked, when will the world's supply of oil be exhausted?" wrote the MIT economist Morris Adelman. "The best one-word answer: never." On its face, this seems ridiculous--how could a finite stock be inexhaustible, when a constantly renewed flow can run out? But more than a century of experience has shown it to be true. As a practical matter, we know only that there is more than enough for the foreseeable future. That is, fossil-fuel supplies have no known bounds. In strict technical terms, this means they are infinite. Hardly anyone who is not an economist believes this, though."