For fuel purchases I recommend looking at the fleet gas cards first. There is a good chance that the fleet cards will give you a bigger discount at the pump than the bonus points. For example, this random link: http://www.csifleetfuelcard.com/ has the quote: Fleets realize up to 15% Fuel Savings with the CSI Fleet Fuel Card.

15% off fuel might be 10% more than the best bonus point card out there.