What is highest gas mileage car to date?

Over 2.6 million.

see link below

The Nissan Leaf electric gets a comparable 106 city 92 highway.

The Toyota Prius Hybrid gets 51 city 48 highway.

The VW Diesel Jetta, Beetle, & Golf vehicles gets 38 city 46 highway.

The natural gas Honda Civic gets 36 city 44 highway.

The gasoline Toyota Echo gets 35 city 43 highway