Most gas places that I´ve used usually put a $1 authorization only. Some rental car companies are bad, they put a big authorization ($350 for a 2 day Thrifty rental in MHT a couple of weeks ago), and then charge the actual rental on top of that. I think it took 10-14 days for the $350 to get released.

This can be a real hassle if you have a card that is close. For example I´ve had Priceline hotels put $100-$150 hold on a credit card for incidentals. My MHT trip, after the hold by Thrifty, I only had $150 limit left (I had spent a bunch on 3 tickets to EZE this summer), so told them not to put a hold on anything. No problem, they said.

Most holds expire at the 14 day mark.