1. Driver Rewards
BP has a Driver Rewards card. It's not a credit card and free to join. Whenever you buy 20 gallons (and a minimum of two visits) you get a reward of 5 cents per gallon off your next visit (up to 20 gallons).
Note: for our family and friends living in NJ we have had pump attendants answer "no" when the screen on the pump asks if we want the reward. You have to tell them if you want them to answer yes or no.
I believe Shell also has a Rewards Card.
2. Credit card rewards
Several of our credit cards will periodically give 5% back on gasoline purchases, so we keep track of which card has the reward. For several if these cards you have to sign-up online and the reward usually goes for a few months. Even though prices for paying with cash are less at some stations, the 5% back on the credit price is often less per gallon. Do your math!
3. Cash back credit cards
Some credit cards will give you 5% ( or other percentages) on gasoline purchases all the time. We keep track of which cards have these too!
4. Driving methods
Of course, using cars as little as possible, combining errands, working from home when possible, and driving habits (e.g. Not always starting out like you're in a drag race) help too!
What ways do you save on gasoline?