Oh, I should have specified. I meant that you can buy 100, 500, or 1000 gallons on credit at a certain gas station at one flat rate. Say it goes down to 2.30, and you buy 1000 gallons. The next month it goes all the way up to 3.15. You still will get your gas for that 2.30 (already paid for) and won't be upcharged to the contemporary price. I recall several news stories of people doing that before Katrina.