I don't think they're processed the same.When you charge at the pump, they send a $1.00 charge through immediately to make sure your card won't be declined. This charge later changes to the amount of purchase. That right there tells you that pay at pump charges are handled differently.
$100?!? Where do you live? Are you sure you're reading that charge correctly? You must live in an area with a high risk of drive-offs, lol.
Preauthorization for Gasoline Purchases