A growing number of oil-industry chieftains are endorsing an idea long deemed fringe: The world is approaching a practical limit to the number of barrels of crude oil that can be pumped every day.

Some predict that, despite the world's fast-growing thirst for oil, producers could hit that ceiling as soon as 2012. This rough limit -- which two senior industry officials recently pegged at about 100 million barrels a day -- is well short of global demand projections over the next few decades. Current production is about 85 million...