If you’re talking fuel economy, diesel wins. We achieved 21 mpg in the TDI, which is 24 percent better than the 17 mpg we saw with a 3.6-liter V-6 and 31 percent better than the 4.2-liter V-8’s 16 mpg. In straight-line runs, the diesel lags behind both gas engines. When the V-8 passes the quarter-mile mark at 15.6 seconds, the gas V-6 is 0.4 second behind, and the diesel trails the gas V-6 by an equal margin. All Q7s feature a smooth, cruising-friendly ride and good forward sightlines from an elevated driving position.
Source: Car and Driver