A lot of people in the comments here are talking about transaction fees.

Just a quick note on that for anyone who might not know - Credit card transactions have fees associated with them that are unknown to the card user. These fees are typically 2-3% plus a flat transaction fee of $.10-$.50, and are billed to the retailer. So while you may be paying $30 at the pump, the gas station is only getting $29 of that, give or take.

Bitcoin will allow you to pay $29 at the pump and then a small transaction fee. So your gas will be cheaper even with the fee.

The much bigger challenge is the transaction time. Credit cards are near instant and it's going to be a major hurdle for mass adoption of bitcoin until the transaction time is much faster.