I completely agree with Dalet that MTBE was harsh on the environment. It needed to be eliminated from our nation's fuel supply.
But from what I've learned ethanol carries its own environmental impact. It takes huge quantities of fresh water and energy to produce ethanol, more energy than is gained. Much of the ethanol is produced near the corn growing areas of the upper mid-west. That region is dependent on the Ogalla Aquifer which needs to be preserved for fresh drinking water and food production. Likewise corn is highly in-efficient in the production of ethanol as compared to sugar cane.
From what I've read the small airplane pilots will not use ethanol blended fuels because of its detrimental effects on the fuel system. Many of them would prefer to use un-leaded fuel instead of the low lead aircraft fuel but they are finding in increasingly difficult to buy clean un-leaded gas and grossly expensive to buy low-lead because it has to be imported into our country now. Their solution is to have a relaible supply of E0 fuel widely available.
Also because of its nature ethanol can not be piped. It must be transported by rail or truck which again is a more expensive means of transpotation. Another in-efficiency in the system. Although the railroads are quite happy about it.
It is my opinion that we really do not need either MTBE or ethanol in our nation's fuel supply because automotive technology has advanced so far that emissions are the lowest they have ever been. However there are those that want to buy ethanol blended fuels and I'm not advocating its total elemination. I just want the choice to buy either product rather than being forced to only buy one.
Marathon makes a fine low sulphur E0 90/91 octane gas that meets EPA air quality standards for large metro areas. My vehicles run very well on this product and have no problems passing emissions.