Infiniti doesnt advertise our vehicles as fuel efficient. They are considered a high performance engine that requires the use of premium fuel. So they really would have no liability against people not getting exact numbers because they never came out and said "most fuel efficient in its class" like hyundai has. I can still get 27-28 on the interstate though, which is actually higher than my car is rated for.

 

The best highway millage readout I've gotten from my x driven on relatively flat terrain is 27.5 mpg @ ~70 mph. Thought it was pretty decent for a 328 hp AWD car, but the actual calculation usually returns 1-2 mpg less than the on-board computer indicates. Is it just my car or everyone else here just reads the number off the Navi screen?

 

I have the x also and only manage 21mpg driving 80% highway. A bit less than the 25 rating but I go 80 mostly so I figure its that.

 

I get 300 miles off 17.5 gallons .80% city but I let it rip on the freeway so thats 100% city

 

Mine is calculated. I use fuelly dot com. Whether calculated or by car computer, they're always very close in my case.
You're getting a little better hwy mileage than I did with my 07X. That's good to see.