Maurice Mugatha slides a long wooden stick into a small hole in the ground at the Exxon station where he works in Potomac. Beneath him is the station's reservoir of unleaded gasoline.

Mugatha bends down and pulls up the stick, which is marked like a ruler.

"Fifty-seven inches," he said, smiling. For a service station that ran out of gas Friday afternoon and did not receive a shipment until Saturday night, this is good news. "We'll be good for a couple of days."

Like many stations in the Washington area, the Exxon in Potomac has struggled to keep a steady supply of gas in its underground tanks because of distribution problems related to Hurricane Katrina. The station's suppliers are giving the station only a fraction of the gas they used to ship, and it is uncertain how long that will continue.

Every day, Mugatha dips the stick into the tank to see how much is left and then informs the supplier. When the shipments arrive, each one costs several thousand dollars more than the last, leaving knotty questions on how to price it for the consumer.

"You basically are at the mercy of when they can deliver your product," said Rick Levitan, who owns two stations in Howard County and one in Baltimore. All have run out of gas at times over the past several days and have been replenished.

Some suppliers are telling stations that they do not know when the next shipment will come in, which leads the stations to increase prices. When stations sell out of gas, they suffer because customers are not coming in the door as often to buy Gatorade and Hostess cupcakes or to get their cars washed.

Retailers say they cannot help but increase their prices after suppliers raise theirs because they have fixed costs they must cover. Besides paying their workers, they have to pay fees to credit card companies for processing payments from customers.

Most card firms take about a 3 percent fee on sales, said Paul Fiore, director of government affairs at the Washington, Maryland, Delaware Service Station and Automotive Repair Association. With gas at $3 a gallon, that comes to about 9 cents a gallon. Gas stations make 8 to 12 cents on every gallon before accounting for the fees, he said.

Business was slow yesterday at many stations in the Washington area, as motorists were not expected to return from vacations until later today and many residents decided to stay home. The average price of regular is about $3 per gallon, according to AAA Mid-Atlantic, which does not compute specific figures over the weekend. Many stations were advertising at more than $3 per gallon, in many cases at $3.20 to $3.50.

"Our hope is the prices will recede as rapidly as they've increased" in the past few days, AAA spokesman John B. Townsend II said. He was not optimistic that relief would come soon. After Labor Day, demand for gas usually drops off, but the past week has proved that many assumptions about the market are no longer true.

"People are lining up to buy gas at $3.50 a gallon," he said. "Have we got more to go? We'll see."

Station managers are hearing fewer complaints from customers in Potomac, many of whom pull up in sport-utility vehicles or sedans and fill up on super or premium. Regular self-serve gas was selling yesterday for $3.49 at the Exxon in Potomac, while full-service regular was priced at $4 a gallon.

Last week, some customers got nasty and demanded to speak to the manager for an explanation of the rising prices. Mugatha, 23, a University of Maryland student who has worked at the station for four years, said he does not even understand the way gas prices work, so his manager has been working the cash register.

His manager, whom he describes as old fashioned, "limits my knowledge" about how he figures the prices, Mugatha said. "I would love to find out."

For now, he simply smiles, greets the regulars who come in and apologizes when he can.

As he speaks, a shiny silver Mercedes-Benz SUV pulls up, followed by a black BMW. Mugatha said, "This is a high-end area, so people still buy premium," which was selling for $3.69 a gallon. "They buy Suburbans and they complain about the gas at $120 to fill it up."