Sorry, I'm in Canada and I got mixed up with US gallons and Imperial gallons. You're right its rated at 21 mpg (US gallon).However, I still think it is low.

I've had my 2009 Vibe for 4 months and 2 of my center caps have been lost already. Anyone else find they fall off easily?

I don't have the GT, but I hae the 2.4 engine. If I had known the mileage would be this poor I would not have bought this car. Very dissappointed. Its rated at 29 mpg and I get 20 mpg (city).