2009 Modell 1.8 petrol. 7.9L/100km equals 35.8 miles/UK gal and 29.8 miles/US gal.
Values are calculated (not driving computer, which btw shows 8.0L/100km)

 

I have an 2006 2.0D Sport. I get about 42/43 mpg with a mixture of 5 miles commute to station and 25/30 mile trips. Interestingly long motorway trips I get about the same unless I try very hard and stick at about 60mph when I managed to get 53mpg but that is too painful so I havent done it again!!

I usually fill up once a month and make a note of the trip computer and mileage between fill ups and I can say that the trip computer is wildly out, about 15-20% optimisitic. My trip computer reads in l/100 miles but I understand from a colleague that newer models have mpg. I asked at last service and they told me it cant be converted nor can it be adjusted to be accurate (which i dont believe).

 

I averaged 27 mpg on my first tank to measure it. That's all US gallons.

[edit] 2.3L Mazda5 Sport, gasoline, 20,000 miles.

 

That's about right for the first tank or so the engine will still be tight yet, mine took about 10,000 mile to fully ease up and I now get consistently good MPG about 36miles to a US gallon (45.9 MPG UK)

 

Did 300 miles on the motorway at speeds of 85mph. Averaged out at 35.8 mpg.