That figure isn’t too much of a surprise, considering that the Sonic is carrying the same powertrains found in the Chevrolet Cruze, which gets a maximum rating of 24/36 mpg city/highway. A Cruze Eco model is estimated to get 28/42 mpg, but those numbers haven’t been finalized by the EPA. The Sonic’s predecessor, the Aveo, achieved a 27/35 mpg maximum rating, with a manual transmission.
Overall, the Sonic’s 40-mpg figure, which is assumed to be highway gas mileage, would be on par with the Ford Fiesta and better than the Honda Fit or Toyota Yaris.