Like a lot of small-scale entrepreneurs, Cathy Osborne worries that she’ll go out of business if fuel prices rise above $4 a gallon. Not because she won’t be able to buy gas at that price, but because she won’t be able to sell it.

The old mechanical gas pumps with scrolling dials at her country store in Fauquier County, Va., lack the gears to go beyond $3.99 a gallon. State inspectors shut down her diesel pump several months ago when the fuel topped the $4 mark, so now all that’s left are two pumps dispensing 87-octane gasoline, set at $3.75 - and climbing.

“I don’t know what I’m going to do. I don’t have $30,000 to invest in new pumps, and I’m barely skipping by,” said Osborne, who owns the Orlean Market and Restaurant, a store dating from 1892 with horse-country views of the Blue Ridge Mountains and miles of rolling Virginia Piedmont.

Osborne said she doesn’t make money on fuel sales, but the pumps are a big draw for the hay farmers and cattlemen who gas up their tractors and take their morning coffee in her store. The next-closest service station is a 40-minute round-trip drive to Warrenton, and in Orlean, Osborne’s barbecue sandwiches and Amish-baked cherry pie face no competition.

“If people have to go into town to get gas, they’ll say, ‘Oh, I’ll just go to Burger King,’ “ Osborne said.

At gas stations in metropolitan areas, digital screens and electronic credit-card readers are standard, but in tiny communities such as Orlean, about 60 miles west of Washington, many mom-and-pop markets are pumping in analog. The dispensers are reliable and retro-cool to some, although their designers apparently never contemplated a future with $127-a-barrel oil.

“We’re one of the few that are left,” said Sharon Hammett, owner of Piney Point Market in St. Mary’s County in Maryland, who said her customers are mostly local watermen. “If it gets too bad, maybe we’ll just pull” the pumps out, said Hammett, unnerved by a recent TV program with apocalyptic predictions of $8-a-gallon gas.

About 8,500 of the 170,000 service stations in the United States are using mechanical pumps, according to the Petroleum Equipment Institute, a trade group based in Oklahoma. Most are in out-of-the way rural areas or at marinas, and not, said executive vice president Robert Renkes, “in the middle of downtown Washington.”

Regulators take a dim view of the obsolete machines, no matter how quaint their surroundings, if the spinning numbers don’t accurately reflect what’s going into gas tanks.

Osborne has run afoul of the rules in the past. When gas prices went beyond $2.99 a gallon, she posted a printout of the day’s gas prices and divided the per-gallon price on the pump display in half, notifying customers that the cost would be doubled at the cash register. Some of the Latino laborers who work on nearby farms had trouble understanding the system at first, she said, but eventually got used to it.

It was an out-of-towner, she suspects, who turned her in to Virginia’s Weights and Measures Association. She paid $800 for a kit to give her pumps the extra digits and gears to go from $2.99 to $3.99.

And now, they’re nearing obsolescence. Osborne said she called a service station supplier last week thinking she would be able to upgrade with another kit, but she was told there was nothing available. State regulators don’t seem to be in a sympathetic mood, either.

Robert Bailey, program manager for Virginia’s Office of Product and Industry Standards, said that it’s a matter of consumer protection. “I think any savvy business owner would have recognized early in the year that gas prices are rising, and there are companies that provide services to renovate or replace analog pumps with digital ones,” he said.

At least one company is working on a conversion kit that will allow the pumps to go above $3.99. But orders are backlogged for months.

That’s why some pump owners have given in and shelled out the money for a digital upgrade.

“You’re either gonna sell gas, or you’re not,” said Greg Fauver, owner of Gore Grocery. He spent several thousand dollars to install computerized displays on the six pumps outside his small market north of Winchester,Va. He figures he spends more on electricity for the pumps than on the gas they dispense, but, he said, “They’re a draw for the store.”

For the companies that sell, service and install gas station equipment, it has been difficult to keep up with demand.

“Some of these mechanical pumps have been unchanged since the late 1940s and early 1950s,” said Luke Neff, sales manager for Service Station Repair in Winchester. “I just don’t think when they were built that anybody fathomed the price of fuel being what it is today.” Neff said his company sells a basic replacement pump for $3,000 to $4,000, plus installation. That doesn’t include upgrades that might be needed.

“It’s unfortunate that a lot of mom-and-pops are getting squeezed out,” he said. “But they’re not doing enough volume to afford to upgrade their equipment.”