Sterling, which airline(s) do you have miles with? It's fairly easy to do with both United & American. Go into the FF sections of the website for the airline you want to use and keep clicking under redeem miles until you get to hotels/cars rather than flights. I've used miles for hotels but not yet for cars. It looked to me like it wouldn't be a bad deal for a one-day rental when rates are high (like $100+ per day) but you'll use a big chunk of miles for a week...My guess would be 40-50,000 miles for a smaller car for a week. Not exactly a great deal. But 5,000 to save $100 on a one-day wouldn't be bad. It looked to me like you'd be stuck paying cash for any taxes/fees, would could still add up to a big chunk of change (this week I paid $140 for a 2-day rental in Houston...$45 per day for the car and $50 in mostly fees and maybe $10 of that actually in tax)