1. Toyota Prius

Average fuel economy: 55.59 mpg
Estimated annual fuel cost: $596

Since its remake in 2004, the Prius has become the most popular hybrid by far, and as of now, it's still the only pure-play hybrid available. Other gas/electric combinations, including the other three on this list, are variations of conventionally powered models. The internal-combustion 1.5-liter four-cylinder engine in the Prius produces just 78 hp. Even though its fuel tank holds only 12 gallons, this hybrid has a range of more than 600 miles. Like the Camry Hybrid, the Prius can run on electric power alone during light-to-moderate acceleration from a stop and up to speeds of around 35 mph.

• See photos of the 2007 Toyota Prius
• Read a review of the 2007 Toyota Prius
• See more Toyota models
• See the Least Fuel-Efficient Vehicles of 2007