Just like with any of our competitors, pre-authorization charges ensure that funds are available for the purchase. It never charges that amount, it is merely just a hold until the total amount of the sale is known. Some financial institutions take longer to release the pre-authorization than others.
The detailed explanation for those with a little more time:
When you pay at the pump, there is no way to know how much your transaction will be, and there is no way to put the product back if your card does not accept the dollar amount. Therefore, when you swipe your card at a pump (whether at Family Express or a competitor), it checks to see that the card is eligible for use by preauthorizing a set dollar amount.
If you were to reach the preauthorization amount the pump would automatically turn off since that is all the card has approved for the transaction, so Family Express has set the preauthorization amounts at $75 for debit transactions and $100 for credit transactions which act differently and convert to $1 that you'd see on-line. When you return the nozzle after pumping your fuel, a message is automatically sent to release the preauthorization amount and charge the actual transaction amount.
The preauthorization amount is never paid to the vendor (Family Express®) it is merely held, pending the actual transaction amount. How quickly the preauthorization amount is released to your account is entirely up to your financial institution. Most banks should release debit preauthorizations immediately but it may take two to three business days. It sounds like your bank releases within hours, but not immediately when the release message is sent.
You may wish to contact your bank and speak with someone in the Debit Department to see if they can give you a more precise answer of when and how often they process those types of preauthorization releases. There are likely different answers to this question depending on if you choose credit or debit at the beginning of your transaction, so it may be that changing which you choose is better for your situation.
Without having spoken to your particular financial institution, I would suggest you either prepay inside the store for an amount of your choosing (which eliminates the preauthorization process completely) or choose "credit" at the pump. I'm told the $1 credit preauthorization amount often stays on your account longer than the $75 debit preauthorization, at least at most banks, but $1 is less noticeable for that amount of time.