I live in Northern Colorado, and I always get my fuel at stations that sell real gas, or
unblended gas. In the cities, the gas "blends" change with the seasons - that is why you hear about
"winter" blend and "summer" blend. You get
worse FE using these blends, and it varies with the winter/summer blends on how bad it gets. They have these blends to reduce emissions in their areas. You will gain FE if you can find and use unblended gas. I was able to
break through 60 mpg by using unblended gas. Good luck figuring out what stations sell "real" gas. The octane ratings remain the same whether you use winter, summer, or unblended gas, BUT your mileage will vary with each.
9NEWS.com | Colorado's Online News Leader | 'Clear gas' hard to find
Lots of articles if you google it.