[regularperson]

This can really be a problem w/ debit card use. Swipe the card and they put a hold on about $100 dollars, so they make sure there’s enough in the acct. to cover the purchase.
If you then buy $20 worth of gas, that’s what’s shown on the statement, but it takes about a day to get the ‘hold’ money credited back.
Same holds true if using a debit card to secure a hotel room. They put a hold on more money than the room usually, and it doesn’t get credited back until after your stay.

[Alberta's Child]

Exactly. A fuel purchase is one of the only credit card transactions in which the authorization is provided before the buyer and seller actually know the exact amount of the purchase (the hotel process you cited is another good example), so this "pre-authorization" has to provide the retailer with some level of protection to cover the uncertainty of knowing how much the actual charge will be.