New York--Drivers shouldn’t hold their breaths waiting for prices at the gas pumps to fall as sharply as the price of a barrel of crude oil.

Oil is down more than 30% since hitting a high of $147.27 on July 11. It's now flirting with the psychologically important $100 a barrel level, a price not seen since April 2.

Meanwhile, the average price of a gallon of gas in the U.S. has fallen just 11%, from a high of $4.10 on July 6 to about $3.65 earlier this week.

A little math shows that if the price of gas had fallen at the same 30% rate as oil, gas would now be below $3 a gallon--down to about $2.90.

So why the disparity?

Tom Wallin, president of Energy Intelligence, which publishes newsletters and data related to the oil and gas industries, said the answer is fairly simple: gas prices didn’t rise as sharply as crude oil prices earlier this year, consequently they didn’t have as far to fall.

But falling they are, and much of the decline can be attributed to simple supply and demand.

Since the price of gas shot up to over $4 a gallon across most of the U.S. earlier this summer, Americans have been driving less.

Consider that in the nine-month period from November to August, Americans drove 53.2 billion fewer miles than they did during the same period a year earlier, according to the U.S. Department of Transportation.

“Demand is off in the U.S. because people are driving less, and with lower demand that effects the competitive price,” said Wallin.

In other words, as drivers have scaled back their miles, the demand for gasoline has fallen off accordingly. With demand down competitive pressure has forced the oil companies to lower their prices.

The wild card, of course, is a natural disaster that could impact production in the refineries that line the Gulf of Mexico from Louisiana into Texas.

If Hurricane Ike, which is currently bearing down on Texas, causes extensive damages, Americans can expect to see a  spike in gas prices, even as the price of crude oil continues to fall.

Tom Kloza, chief oil analyst at the Oil Price Information Service, explained that widespread damage could push the price of crude lower because damaged refineries lead to reduced demand for crude oil. (If there’s no place to refine the oil, global demand falls off and with it the price.)

Meanwhile, the price of gas shoots higher in the U.S. due to shortages of the refined product used to make gasoline.

“We have the true bipolar market,” said Kloza.

Kloza said he wouldn’t be surprised to see gasoline rise up over $4 a gallon in many states “on a temporary basis” (his emphasis) as the threat of hurricanes hovers off the Gulf Coast.

There’s hope in sight, however. 

If, as many expect, oil falls to the $80-a-barrel level after the threat of hurricanes dims, there’s a good chance the price of gas will drop again. Wallin said it might drop another 10% or 20% from its current levels, which would put it in the $3-a-gallon range.

“But these things are always very hard to predict,” Wallin cautioned.