http://www.amexoffers.com/

T&C:
ELIGIBLE PURCHASES: Offer valid for purchases at gas station locations in the U.S. An "eligible purchase" means a purchase made with your enrolled Card at U.S. gas station locations by 12/31/2018. Offer excludes online purchases and marina fuel or any type of commercial fuel (e.g.- jet fuel) purchases. For purposes of this offer, "gas station" means a merchant that is in the primary business of selling gasoline to consumers. Gas stations may sell other convenience items, but its primary business must be selling gasoline to consumers. The following are NOT considered gas stations: superstores, supermarkets, and warehouse clubs that sell gasoline.