Crucial step: After setting the rear view mirrors, checking your maps and heading out of the rental car parking lot, you must--I repeat MUST-- look for the nearest gas station. While you'll likely want to gas up further from the airport (to get a better price) when you return the car, things can go wrong, schedules shift and many drivers forget to fuel up, and so leave it up to the car rental company to do.
But no more.
With rental car rates for fuel reaching $9 a gallon, not even Warren Buffet can afford to leave the re-fueling to Hertz (which now charges $9.29/gallon according to USAToday) or Enterprise or Thrifty ($8.99 each).
In the same article, USAToday reports that of the 102 prepay options available to consumers from the various companies, 54 turned out to be cheaper than refilling the car oneself at nearby gas stations, the others not. But that estimate was based on refilling an empty tank, which is what you pay for when you pre-pay. Most renters have half a tank or more of gas left in their cars when it comes time to turn them in.
So is the greed, or a preview of what's to come for all drivers? I'm coming down on the side of outrageous, unmitigated greed. There's no way the rental car execs can know, definitively, which way the cost of gas is heading. They're taking advantage of the current problems to line the company's pockets.
Don't let 'em do it! Fill 'er up!