Prepaid gift cards work at gas stations if cardholders can input a ZIP code at the pump; some cards, like the OneVanilla card, allow cardholders to select a ZIP code for authorization purposes. Cardholders can also bring the card to the clerk to prepay and sign.
Gas pumps are automated, so there's no way for users to sign for their purchases. To verify that the person using the card owns it, gas pumps often ask for the ZIP code. Online sellers sometimes use a ZIP code to verify ownership of a card as well, so buyers should determine if the card they're considering can support ZIP code authorization if they want to make online purchases.