We have a 2016 Volt Premier we purchased in June 2016 now closing in on 10,000 miles, my wife's car. I noticed that the last month or so when running just on gas, reg. 87 octane with 10% ethanol (winter blend), the Volt has averaged 45.5 mpg. Now our 2010 Prius, same fuel, same time frame, last fillup, calculated of course was 43.5 mpg. Yesterday with dry roads and temps in the high 30's to low 40's are nearly 100 mile round trip we averaged 48 mpg on the Volt. I now have noticed that the Volt when running just on gas in the winter does not take a big hit on mpg like our Prius does. Now the Prius in summer is always mid 50's to near 60 mpg, quite a big swing. I wonder if any forum members who own both a Prius and 2nd gen Volt have noticed the same issue.