I suspect that no reasonable person would consider a new MX-5 to be an
economy car or give the fuel economy a huge role in the decision to buy
one but I thought that this might be of interest. Immediately after
getting my "break in" miles put in on my '06 Sport with handling option
done I drove up to Pennsylvania to visit my mother over Easter. The
mileage between here and there is virtually all interstate -- just short
of 500 FWIW.

I knew what sort of economy my '91 Miata had consistently achieved on
the same trip and expected the new one to get just a bit worse or, with
luck, to achieve the same. Here is what happened on four fillups that
were on the interstate mostly at 70-75 under cruise control: 32.0, 33.9,
35.1, and 32.7 MPG. I was truly shocked by those results but calculation
of the overall consumption since delivery, including 1,800 miles of
city, suburban, and interstate driving shows that it has been getting
30.7 MPG. I realize that the four interstate legs might be skewed by the
imprecision of how consistently I was able to fill the tank each time
but the overall figure should be relatively accurate.

BTW: the interstate miles were done with 30psi in the Michelin tires
rather than the recommended 29psi but I don't know how much that might
have affected the economy.
--
John McGaw
[Knoxville, TN, USA]
http://johnmcgaw.com