Here's another issue for refiners to concerned about: liability. Both Valero, the largest U.S. refiner, and Marathon Oil Co. have expressed concerns that selling gasoline with increased ethanol content may leave them liable if long-term engine damage occurs. The EPA's decision on raising the allowable percentage of ethanol in gasoline has come, but without liability protection, refiners may choose to stick with the proven E10. Indeed, refiners have no obligation to blend E15 and may choose never to do so, but we'd bet that the EPA will find some way to entice refineries to make the switch. That is, if it ever grants E15 as an approved blend for more vehicles.