Why does my card get declined at gas stations?

Gas stations pre-authorize cards for a fixed amount (often $100–$150) to cover the maximum possible fill-up. If your available balance or card limit is less than the pre-auth amount, the card will decline even if you only plan to spend $30. Solution: make sure your available balance exceeds the pre-auth amount before fueling, or pay inside and ask the attendant to run an exact amount.