The Aveo is rounded and more aerodynamic than the brick-shaped xB.
The Aveo is considerbly lighter than the xB.
The Aveo is geared lower than the xB in top gear.
The engines are very close in size, 1.5-1.6 liters.
Why does the xB beat the Aveo?
Better engineering woot woot.
The Aveo is supposed to get 1 more highway mpg than the Xb. It looses this advantage around town by a surprising 4 epa mpg
DOH, that is supposed to be 34 highway mpg for the xb