To be sure, as Mr. McClellan said Wednesday, there is more to President Bush's energy policy than seeking to ensure surplus capacity. The administration has called for increasing domestic production and refineries, development of alternative and renewable fuels, expanding nuclear energy and, recently, greater conservation. Still, the Persian Gulf countries are seen as crucial in moderating future prices.

During the 2000 presidential campaign, when high gasoline prices were an issue, Mr. Bush pledged to do a better job of influencing Persian Gulf producers to pump more oil.

Early on, the administration was mostly interested in whether the Saudis would produce more oil during the anticipated conflict in Iraq. Long before the war began, Saudi spare capacity -- roughly three million barrels a day above the seven million barrels being pumped daily in 2002 -- seemed adequate.

Productive capacity depends on the amount of oil in the ground as well as the infrastructure required to drill, process, store and transport the oil. In addition, increasing capacity is very costly and time-consuming.

"The long-term capacity was not considered a problem," said Robert W. Jordan, the American ambassador to Riyadh from 2001 to 2003. The Saudis, he added, "never expressed any concern about the need to expand."

"Nor did we, or at least me, engage them on this topic," he said.

In April 2002, when President Bush met Crown Prince Abdullah, now the Saudi king, the focus was not on oil but on Israeli-Palestinian matters, according to Mr. Jordan. The United States did not press the capacity issue because, even two years later, Saudi officials were publicly expressing confidence that there was no need over the next five years to add capacity.

Going to 12 million or 15 million barrels a day was possible, though, because the country had an estimated 150 billion barrels above the 260 billion in proven reserves, Nansen G. Saleri, a senior Saudi oil executive, said at an oil conference in Washington in February 2004.