Late winter, early spring conditions, not optimum for mpg's, here in Northwestern Oregon. The last fill up with our 2010 Prius, calculated, 46.2 mpg. Now our 2016 Volt has beat that, so far for the last trips on the gas engine averaged 47.554 mpg, calculated, (518.3 miles / 10.899 gal's (87 octane Costco reg. gas w/ 10% ethanol blend and winter formulated gasoline). Both the Prius and Volt use Costco 87 octane gas. I have noticed since Chevy did a recall update (software computer) on our Volt's gas engine, it now runs smoother and delivers better mpg's than before the update. I would say 3 mpg's or more than before. Just seems like pretty good mpg for a car like the Volt that weighs, with a couple of full size, driver and passenger, in the car for a car weight of over 4,000 lbs, plus the benefit of driving 45 miles (in winter) to over 60 miles(summer) on just electricity.