My experience with National has been they charge the amount of the rental when I pick up the car and there is no deposit. I believe the credit card shows it as "pending" or something until the car is returned and then goes as a regular charge. I'm not sure if this is an Emerald Club policy, but it is one policy I like about National.

I know Avis puts a hold of the estimated rental cost, or $200, whichever is higher, and then credits back the difference when you return the car. Hertz puts a hold of the estimated total plus $250 and in my experience is very slow to remove the deposit, especially on one way rentals.

With all the holds that are put on credit cards if you rent a couple of cars and stay at a few different hotels during the week you can have a lot of money drawing against the credit limit on your card. I have seen hotel holds linger for close to 30 days, as they keep the hold but charge you a second time for the actual bill. I'm sure it is legal but it annoys me when I see several of these holds on my card on months where I have a lot of travel. I don't want to be checking into a hotel at midnight and have to call the credit card company explaining I'm not over limit if you ignore all of the lingering holds on the card that shouldn't be there.