What production car has the highest fuel economy rating?

There's no single definitive answer to what production car has the *absolute* highest fuel economy rating because ratings vary depending on the testing agency (EPA in the US, WLTP in Europe, etc.) and the specific model year and trim level. Fuel economy also depends on driving conditions.

However, consistently at the top of the list are several models of hybrid and plug-in hybrid vehicles, particularly from Toyota (Prius family) and Hyundai/Kia (various hybrid and plug-in hybrid models). Small, lightweight vehicles also tend to achieve very high MPG ratings.

To find the most current highest rated vehicle, you'd need to check the latest fuel economy ratings from the EPA (for the US market) or the equivalent agency in your region.