It's a base 2016 XC70 T5 five-cylinder, no Polestar - I use premium gas - on the highway at 64 mph, the average hovered between 33.8 mpg and 34 mpg, was at Hartford at 34 mpg average. I am very impressed with that, did not think it would be so high, but then I deliberately drove 1 mile below the speed limit to see what would happen.
On the highway, I generally do 75 to 80 (like everybody else), and get lots of 26.6, 26.8, and the occasional 27 mpg.
i live in a semi-rural, hilly area, and driving around town and on back roads I average 20-21, a lot of 20.6 and 20.3 and so on.
Since I am not on the highway that often, the overall has been around 21-22.
I am seeing similar results in my wifes 2016 xc70 t5 awd. Also run premium gas and keep it in eco mode. On country highways between 55-60mph we see 30-32mpg. Our average on the country backroads near our house is 26mpg.
It consistently gets at least 4mpg better than my 2006 xc70 in the same conditions. The extra gear in the 2016 and eco mode make for a downright thrifty road trip machine.