Some oil executives are sounding the alarm bell. At a recent energy conference, John Hess, the chief executive of Hess Corporation, the international oil company, warned that an oil crisis was looming if the world didn’t deal with runaway demand and strained supplies. The chief executive of Royal Dutch Shell, Jeroen van der Veer, said recently, with some understatement, that, “the energy outlook does not look rosy.”

For one thing, the world’s oil supplies are already stretched. Countries outside of the OPEC cartel  which have been the main source of new oil discoveries and production since the 1970s  have said they expect little to no growth this year in oil production.

The North Sea and Alaska are slowly running out of oil and producers there are struggling to keep production from falling. Russia’s phenomenal oil surge is coming to an end; a top executive of Lukoil, the country’s second-largest oil group, said last week that the country’s production was unlikely to grow much. Nigeria is battling a violent militancy. And Mexico, the third-most-important supplier of crude to the United States, has been stuck in a crippling political debate over keeping out foreign investors while witnessing a dramatic drop in production that some analysts say may be irreversible.

What about OPEC? The 13 members of the Organization of the Petroleum Exporting Countries account for three-quarters of the world’s proven oil reserves. But for various reasons, most of those countries are making it harder, if not impossible, for foreign oil companies to invest within their borders. With energy prices rising, OPEC producers are seeing record revenues, which have reduced the incentive to dip into their supplies by boosting production.

At the same time, major oil companies like Exxon Mobil, BP and Chevron are finding it harder to compete worldwide, as national oil companies erode their once-dominant positions. Fourteen of the world’s Top 20 oil companies are state-owned giants, like Saudi Aramco and Russia’s Gazprom. That leaves Western oil companies in control of less than 10 percent of the world’s oil and gas reserves.

Facing higher costs, those companies are also having greater difficulty locating new oil deposits. Despite spending over $100 billion on exploration last year, the five largest international oil companies found less oil last year than they pumped out of the ground.

A small band of skeptics view today’s record prices as evidence that oil supplies have peaked  that half the globe’s oil supply has already been used up. But most experts believe that there are still enough oil reserves, both discovered and undiscovered, to last at least through the middle of the century.