The number of TVs atop gas pumps has leapt since their introduction at a handful of stations. Now, three companies have placed more than 20,000 screens at thousands of stations from the Massachusetts Pike to Southern California.

"We try to bring some fun to the pump," said Roy Reeves, vice president of sales and marketing for PumpTop TV, an Irvine, Calif., company that provides screens and content at nearly 600 stations nationwide.

Fun at the pump. When was the last time you heard someone say that?

The TVs also bring in money for gas retailers, who have seen their margins shrink because of an increase in fuel load costs and credit card fees.

Gas Station TV says that stores with screens on pumps report selling 75 percent more car washes and 69 percent more snacks if those items are advertised.

TV programming at the pumps varies by location and provider. PumpTop TV, for instance, provides real-time traffic maps, local sports scores, headlines and weather. Fuelcast carries trivia and NBC content. Gas Station TV broadcasts CBS programming and carried an American Idol-type search earlier this year for a host who will anchor some segments.

All offer heavy rotations of 15-second ads, and all say they will roll out screens in new markets this summer. Though no revenue figures have been released, all say they are growing.

These companies pay gas-station owners "rent" in exchange for placing the flat screens above the pumps.

Once a customer starts the pump, the TV comes on -- and stays on. There's no way to change the channel or mute the volume. So people usually tune in.

"It's a natural pause point in people's day," said David Leider of Gas Station TV in Detroit. "The customer is tied to the screen with an 8-foot rubber hose for five minutes."

On a recent day at a Shell station in Miami, the Fuelcast screen above the pump aired 15-second ads for fuel-efficient Chevy cars and Norwegian Cruise Lines.

Anna DaSilva, 59, a retiree from Doral, Fla., said she had never seen the screens until this month. DaSilva said she liked the idea because the ads distracted her from the high gas prices.

"I think that's the whole purpose of the TVs," she said.