you guys and your Miles/gallons.....
here in the superior metric system (hehe), i consistantly get 10L/100km
(calculated it this morning, did 480km, to about 44L, so thats even closer to 9.1L/100)
which according to some online conversion guide is about 23.52miles/gallon. (10L/100)
i don't tend to drive like a grandma everywhere either, give it a bit of stick reasonably often. (standard s15, apart from exhaust and a bit of extra boost)
so i dunno how 23.52mil/gal compares to your 30pounds/100miles.
the only real way to check fuel consumption, is to fill it all the way up, hit the trip meter, run it low, then fill it all the way up again, see how much you had to put in, and check your trip meter again.