The 2014 Scion xD is, by now, falling toward the bottom of the small-car pack when it comes to fuel economy. Regardless of which transmission you choose, all xD models get the same EPA rating: 29 mpg combined (27 mpg city, 33 mpg highway). That's not much better than most mid-size sedans these days.
In part, this reflects the car's age; the Scion xD is now seven model years old, and it was more competitive with tall boxy small hatchbacks when it was launched in 2008. But with a new and more fuel-efficient Kia Soul on the market this year, not to mention five-door minicars like the Chevrolet Spark and Mitsubishi Mirage coming in at 34 to 40 mpg combined, the xD is pretty clearly subpar.
We might also assign blame to the car's large and not-very-powerful engine--128 horsepower from 1.8 liters isn't impressive--and its archaic four-speed automatic transmission. At least the base xD with the five-speed manual gearbox is more fun to drive, but either way, there are many more fuel-efficient small cars out there.