Leading players in the petroleum industry, including Saudi Arabia and Exxon Mobil Corp., are aggressively arguing that plenty of crude oil remains for world consumption, in an effort to counter critics who contend crude output is about to plateau. That argument, known as peak-oil theory, has provided intellectual backing for the boom in crude prices and sowed doubts among some policy makers about crude's long-term reliability as an energy source. Such doubts, coupled with concern over sky-high prices, have added impetus to the search for oil substitutes -- including in Washington, where President Bush this year declared the U.S. "addicted...