Vehicle costs: Adds about $2,000 to $3,000, but hybrid models usually have unrelated additional features making it difficult to assess the cost of the hybrid feature alone.
Efficiency: Increases fuel efficiency by anywhere from 25 to 40 percent compared to vehicles with similar-sized gasoline engines.
Fuel costs: Uses gasoline, so reduces fuel costs to the same degree that it increases fuel efficiency
Performance: Depends on the setup. Can actually boost performance while still increasing fuel efficiency compared to a non-hybrid car. But more performance will mean less efficiency.
Greenhouse gases: In any vehicle, CO2 emissions vary directly with the amount of fuel burned, so hybrid vehicles reduce CO2 emissions to the same degree that fuel efficiency is improved.
Other pollution: Reduces emissions of other pollutants to the same degree that fuel efficiency is improved, assuming hybrid and non-hybrid vehicles are otherwise the same.
The future: General Motors is working on two new plug-in hybrid vehicles, but it has not set a specific timeline. A plug-in hybrid could have its batteries charged by plugging into an electrical outlet as well as by using power generated from an on-board engine. The first GM vehicle would be a plug-in version of the new Saturn Vue Hybrid. The other would be something like the Chevrolet Volt concept car, where the wheels are driven by electricity alone, and an on-board engine is used only for back-up generator power.