I do believe it has the option.
I'm uncomfortable with the cars that don't have the cap, only the exterior flap.
Also if you have a single exhaust outlet, the filler neck is almost always on the opposite side.
Most of my chevy 4 cyl I've owned have been on the passenger side... My camaro was behind the license plate ('76).
I too thought it looked like the Sonic had a space for a gas door lock... Wonder why it doesn't other than money because my brothers Spark has a lock with the latch by the driver seat.... Wth? I don't really care but flush without the little bump for your finger looks nice.
Also on my Holden Barina RS a pin locks the fuel door when my doors are locked.
Thanks Kraken... I'll look on my '13 to see if it has that tiny hanger for the gas cap.
Now we know why it looks like they planned on having a locking gas cap on the sonic.
Any way to get a pic of the lock assembly? I wonder if it could be added to the sonic or if we would need a new BCM program.