The sellers affect the futures market by reducing or increasing their throughput, or plausible threats to reduce or increase throughput. They may act individually, or in the case of OPEC, usually in consort. Most items on the futures market may be said to be a situation definable as 'oligopoly'- hog bellies, corn, rice, copper, aluminum, etc., as well as petroleum products.

The supply is also limited by refining facilities, transport, disruption of supplies by events such as war, etc. , but especially by the growth of new markets.

In an article headlining the NY Times 'Week in Review,' April 20, John Hess, CEO of the Hess Corporation, warned that an oil crisis was looming if the world didn't deal with runaway demand that strained supplies. J. van der Veer, Shell Oil CEO, said recently that "the energy outlook does not look rosy."
Suplies are already stretched. Countries outside OPEC, which since the 1970s have been the source of new oil discoveries, have said they expect little or no growth this year in oil production. These countries include Canada, the biggest supplier of both oil and gas to the United States, Mexico (third largest) and Nigeria (4th largest).
The OPEC countries are seeing record revenues, and see little reason to increase production, which in essence mortgages their future.

Fourteen of the Top 20 oil companies are state-owned, leaving western oil companies such as inaccurately maligned Exxon-Mobil, etc., in control of less than 10 per cent of the world's oil and gas reserves. The five largest international oil companies found less oil last year than they pumped out of the ground, despite spending over $100 billion on exploration.

How to save? A few suggestions.
Reduce distance driven 25 percent. For the U. S., the amount saved would be close to the amount of oil imported from Saudi Arabia, Angola and Ecuador.
Combine trips. Plan ahead. Vacation closer to home. Use car pools and public transit if possible.

The article suggests using more diesel vehicles because they are more efficient- but with the demand for air conditioning, room for kids and hockey equipment, etc., This may not help much. Large SUVs are comfortable and roomy, but the new generation of smaller SUVs is excellent (my younger daughter, who needs carrying capacity because she lives in the country, changed from a large Toyota 4-runner to a Santa Fe and saves several hundred dollars every year).

Good article- "The Big Thirst," Jad Mouawad, New York Times, April 20, 2008, Week in Review Section, pages 1 and 4.