This is the only thing I've found so far on a national level and it doesn't appear that oxygenated fuel is required in Iowa.https://www.afpm.org/uploadedFiles/Content/Our_Members/What_We_Make/Fuels/US-Gasoline-Map(1).pdf https://www.afpm.org/uploadedFiles/Content/Our_Members/What_We_Make/Fuels/US-Gasoline-Map(1).pdf