It is unclear how many people are hypermiling. But high gasoline prices are inevitably going to lead some to change their driving habits, said Jake Fisher, a senior automotive engineer with Consumer Reports who has blogged about hypermiling.

Consumer Reports recently conducted tests on hypermiling techniques and determined that some are effective at reducing gas consumption.

The biggest factor in getting better gas mileage is driving at a moderate speed - 55 mph instead of 65 or 75 mph - the publication reported.

When the Toyota Camry's cruising speed was increased from 55 to 65 mph, the car's fuel economy dropped from 40 mpg to 35, it reported.

Other techniques include keeping tires properly inflated and avoiding frequent bursts of acceleration, sudden braking, the use of premium fuel and driving on a cold engine.

Kriston of AAA said hypermiling can undoubtedly be effective at cutting gas use.

"Doing those things, where you're trying to maintain a cruise as much as you can - it does make a difference, it really does," he said.

Hypermilers also use their air conditioning more efficiently, Gerdes said.

He cools his car before he starts the engine by opening windows and doors. Gerdes cycles the air conditioner on and off and recirculates the dehumidified air rather than let the AC run nonstop (or driving with the windows rolled all the way down).

Clark Semmes, a self-identified hypermiler who commutes from Baltimore to New Carrollton two days a week, said he has seen an improvement on the real-time gas mileage display in his Toyota Prius.

He now gets about 55 mpg on the highway, even though his 6-month-old Prius is only supposed to get 45 mpg.

"I don't go so slow that it would be annoying," said Semmes, a founder of the Mount Washington Green Club.

He also shifts into neutral when going downhill and tries to get behind big trucks, although, he said, "I'm afraid to get too close, so I'm not sure it makes a difference."

Semmes is motivated by his concern for the environment, but he also hypermiles, he said, "because it's cool."

Other drivers gave various reasons for starting to slow down.

George Baca, an anthropologist at Goucher College, maintained a speed of 60 mph in his Volkswagen Jetta to and from Philadelphia last weekend. He usually gets about 325 miles from a full tank when he's driving 75 mph.

For the Philadelphia trip, he only used half a tank to drive 215 miles.

"I'm not really perturbed by gas prices being high," Baca said. "I've always thought it ridiculous that a finite resource was being sold so cheaply in the United States."

But he began driving slower long before gas prices escalated, aware that each gallon expended resulted in pounds of pollution released into the environment.

As he filled up his Dodge Dakota pickup at the White Marsh Costco on Monday, Jim Schaffer explained that he used to drive about 65 mph.