It depends on the type of driving undertaken. Petrol Hybrids work well in hilly country and around the city, but it has been proven in real-world tests in this country (Australia) that small(ish)...
The most fuel effincient car is the Honda Hybrid. --- Hydrogen-fueled cars such as the Honda Clarity FCX and new H2 Mazda RX-8 don't even use gasoline/diesel. Volkswagen Lupo 3L uses 78 miles per US...
The Most Efficient Car is The Electric Car sports Car that recently came out. The last answer was terrible so i changed it but this one is probably worse.
GM and ford are the most fuel efficient in terms of trucks and suvs, Toyota and Honda may make the civic and prius hybrids but their engine technology is lagging, the compact Toyota Tacoma pickup...
The answer to your question is very complex and requires more knowledge than the average person has. The Prius is not the most fuel efficient car. the Honda insight is the most fuel efficient car...