Benefits of Registering
If you register, you will be able to save your MPG information and view, edit, or update it later. You will also be able to share your MPG with others. Fueleconomy.gov retains no information that could be used to identify any individual with a user name or password.
As a non-registered guest, you still have access to all MPG tools, but you cannot save your data or share your MPG.