Another poster commented that the decision on whether ethanol is required is made my the states. In some cases, that is true. As an example, I live in Minnesota, which has mandated E10 use statewide in 1997. Non-ethanol fuel is available, but only as premium, and only at retailers who choose to carry it. Surprisingly, the list of states that mandate ethanol isn't terribly easy to determine. The last list I could find stated six states required E10 blends.
The reasons everywhere else went to E10 vary, but originally some of it was driven by reformulated fuel standards. Those originally required an oxygenate, and Ethanol and MTBE were the common choices. MTBE was phased out when its groundwater polluting issues were determined to outweigh its benefits.
The reformulated fuel requirement for an oxygenate essentially went away though when the RFS standard took its place. Essentially, it requires refiners and other non-oxygenate blenders and importers to displace just over 10% of their non-renewable fuels with renewables. That is the reason E10 fuels tended to show up everywhere else - refiners were required to show they were meeting the standard. Not state mandates, but a federal one.
The reasons everywhere else went to E10 vary, but originally some of it was driven by reformulated fuel standards. Those originally required an oxygenate, and Ethanol and MTBE were the common choices. MTBE was phased out when its groundwater polluting issues were determined to outweigh its benefits.
The reformulated fuel requirement for an oxygenate essentially went away though when the RFS standard took its place. Essentially, it requires refiners and other non-oxygenate blenders and importers to displace just over 10% of their non-renewable fuels with renewables. That is the reason E10 fuels tended to show up everywhere else - refiners were required to show they were meeting the standard. Not state mandates, but a federal one.