Dick Jorgenson commutes 90 miles round-trip five days a week between his job in Salt Lake City and his home on a buffalo ranch in Peoa, Summit County.

In addition to the $70 it costs to fill the tank of his sport-utility vehicle, Jorgenson has about 15 other vehicles on the ranch used to transport hay and buffalo.

"Diesel is almost $5 a gallon," he said. "I spent like $175 filling up my diesel truck. I think it's too high."

On Thursday, the price of a gallon of regular unleaded gas in Utah pushed over the psychologically significant $4 mark to $4.01, according to AAA and the Oil Price Information Service. Nationally, the average price for a gallon of regular unleaded gas reached a record high of $4.06.

"Definitely, it has a psychological impact on people," said AAA spokeswoman Cynthia Harris. "What we've noticed is it's changing people's behavior."

People are driving less. AAA found that over Memorial Day travel decreased slightly — by 0.1 percent. It was the first decrease in six years.

"There is a possibility that we may see a decline in Fourth of July travel, as well," Harris said.

People also are driving more fuel-efficient vehicles, sticking to the speed limit, hitting the bakes less aggressively, avoiding driving during peak hours, and driving at times of the day when it's cool and air conditioning is unnecessary, Harris said.

Analysts say oil prices, driven by a declining dollar, are pushing gas prices higher. Oil prices rebounded from a steep early loss to end modestly higher Thursday in another volatile session. Light, sweet crude for July delivery rose 36 cents to settle at $136.74 a barrel on the New York Mercantile Exchange.

Given the volatile price moves of recent days, analysts saw few signs of a changing trend in Thursday's trading. Prices have gone through several sharp swings over the past week, rising more than $16 last Thursday and Friday, falling more than $7 earlier this week, and jumping back more than $5 on Wednesday.

Spencer Nelson, a Payson native who lives in Provo as a student, has eased up on the brakes and the accelerator to save money on gas.

"I do ride my bike to work," he said. "I did that before gas was so expensive, but now there is more incentive."

Kathi Hausen of Sugar House is happy she owns a small Honda sedan because it has helped make high gas prices easier to swallow. Even at $4 a gallon, she can fill up her tank for about $50.

"It doesn't take a lot to power a Civic," she said.