American Express has another promotion offering 5% off all gas purchases at BP until 1/31/2012 when you register your card. It says you must be invited, but these offers are often found via a simple banner link somewhere on their website and usually work as long as they accept your card number. You get the 5% back via statement credit, on top of your existing card rewards. I registered my trusty Starwood AmEx travel rewards card with no issues.
Try yours… it’s worth a shot for an additional 15+ cents off per gallon. If you combined this with the Blue Cash Preferred AmEx with 3% back on gas, you’d be looking at 8% total cashback.
Update: The wording is ambiguous, could mean 5% back on all your purchases for the entire month!