It's late. It's cold. It's wet. Your Nikes have a hole in the sole. You've prepaid the cashier like a good kid. All you want is for the gas pump to hurry up and disgorge all $10 of your precious petrol.

But the pump dawdles . . . 9.80 . . . 9.84 . . . . And it lingers . . . 9.87 . . . 9.90 . . . . Seems like the closer you get to 10.00, the slower the pump pumps. Ever wonder why?

The reason is that the pumps believe in self-preservation.

They're designed to slow the flow of gas at the end of a sale so the pump itself isn't damaged by a sudden shutoff, explained Tom Cairnes of Tokheim, one of the country's largest pump manufacturers.

"So much fluid rushing through a pipe at a high speed -- if you just slam it shut, you run a shock through the whole system," Cairnes said. Therefore, while gas flows at between 12 and 15 gallons a minute for most of a purchase, it automatically slows to between two and three gallons a minute once you get within the last 20 cents worth.

If you still feel put upon, consider truckers. At the diesel pumps where they refuel, "slow flow" starts with 60 cents left. That'll convince you to resole your Nikes every time.