if you run your card as a debit at the pump it pre-authorizes your purchase according to whatever the stations preset is (could be $25, 35, 50, 10,000...whatever the gas stations preset is)

if you run your card as a credit it pre-authorizes anywhere from $1.00 to $5.00 depending on the card, the state, etc and the actual charge will show up 3-5 days later


moral of the story, always run your card as credit at a gas pump....b/c once an amount is pre-authorized it is unavailable until the actual amount clears which may cause you to bounce a purchase