Gas stations are operated as post-pay; it is necessary to perform preauthorization for each transaction. Your bank preauthorizes $1 or $100 (depending on the type of card). The $1/$100 will not settle; instead, it will be removed from your account based on the bank's rules.
Debit and Amex: $100 hold for fuel transactions. This is standard in the industry. Hold releases once the transaction is complete and the actual amount is settled.
All other cards: $1 hold for fuel transactions. This is standard in the industry. Hold releases once the transaction is complete and the actual amount is settled.
Note: When using a debit card at any gas station, you can select credit instead of debit to prevent large preauthorization amounts.