If only oil worked like potatoes.

If the world became gluttonous for potatoes, and farmers couldn't produce enough, the price of potatoes would rise. If the price rose too fast, we'd soon lose our appetite for spuds. Cooks would substitute macaroni or rice or something cheaper. Demand would wane and the price of potatoes would level off or even fall.

That's how the market works for most things, but not for oil. There is no easy substitute for it; you can substitute corn, but it takes a lot of energy to grow that corn, turn it into ethanol and then deliver it to market. When oil prices rise quickly, demand hardly falls at all. When supplies are tight, prices go up and there's nothing to stop them.

In May, the price of gasoline was up 19 percent from the year before, but U.S. gasoline use was down by only 1.4 percent, and diesel use actually rose. It seems we can't sell our SUVs and move closer to work overnight.

Other factors also are at work in the price of oil. Those sharply rising prices have drawn more speculators into the market. Some think speculators are helping bid up the price, but no one has a solid handle on how big a role speculation actually plays.

Then there's the twitchiness that comes with a market in shortage. This week alone, oil prices fell by $9 a barrel on Monday and Tuesday, increased by 70 cents on Wednesday and then bounced up $5.60 to $141.65 on Thursday. All it took was rebel activity in Nigeria and missile-rattling by Iran to create an outsized effect on prices.

This week, The Wall Street Journal quoted analysts who think that oil could rise to $200 a barrel by year's end. Oil at $200 per barrel would mean gasoline at $6 a gallon. Airlines and trucking firms would fall into bankruptcy. Jobs would disappear. Our mini-recession could become a maxi-recession.

There's little that the American government can do about this over the short run. Former House Speaker Newt Gingrich wants Washington to release oil from the Strategic Petroleum Reserve. He says this would shock the speculators out of the market and lower the price.

But the strategic reserve contains only a 58-day supply. We'd blow through it quickly, and then we'd be back in the same spot we're at today. And we'd have a weaker safety net if a calamity in the Middle East should cut off oil imports.

Sen. John Warner, R-Va., has suggested reimposing the 55-mile-an-hour speed limit on Interstate highways, an idea that polls show is opposed by 70 percent of Americans. That may change if gasoline hits $6 a gallon.

Our best ally is time. While oil demand is sticky in the short run, it's elastic in the long run. American demand for gasoline fell by 12 percent during the oil shocks of the 1970s as we downsized from V-8 muscle cars to six-cylinder family sedans and pint-sized Chevettes and Escorts. Over the next few years, we'll be moving to hybrids and battery-powered commuter cars.

Oil demand has been fed largely by the developing world, especially China. China recently raised the domestic price of gasoline by 18 percent. Other Asian nations that subsidize fuel prices may follow suit. Over the long run, that should also slow the growth of demand and ease the pressure on price.

In the short run, China reportedly has been stockpiling oil to ensure no shortages during the Olympics that begin in Beijing next month. Once the games are over and stockpiles are released, that could drive prices down temporarily.

On the supply side, things look uncertain. After holding steady for three years, oil production is up 1 percent this year. Practically every available rig is at work drilling for oil, and today's prices provide powerful incentive. But no one really knows how much oil is out there, and some of the older fields are playing out. Newer domestic supplies — in Alaska, off the continental shelf and in oil shale fields in the west — are fraught with political risk.

The only real solution is conservation. The only sure way to pay less for oil is to use less of it. That makes a lousy campaign slogan, but it's a fact.

REPRINTED FROM THE ST. LOUIS POST DISPATCH.