No, It's down to the formulation. The difference is that Summer and Winter gas evaporate at different temperature ranges. Summer gas in cold temps causes the engine to be rough and hard to start. The trade off is, winter gas has slightly less energy, which is where that minor mileage difference comes into play.I'm no expert, but isn't it likely that such a small difference (1.7%) is simply due to the engine needing more time come to normal efficient operating temperature from a colder starting point? I know when I drive long distances in my car in the winter, the highway range is basically the same, or within a margin of error, and most likely could be attributed due to winds.