Hybrid cars were invented far earlier than most of us imagine. In the late 19th and early 20th centuries, they competed alongside gas, electric and even steam-powered cars for dominance. Of course, gas-only vehicles won the day. But as issues of fuel efficiency and emissions became increasingly important, hybrids reemerged. Newer hybrid prototypes were developed starting in the 1970s, but most never made it to market. The first commercially available hybrid was the Toyota Prius, introduced in Japan in 1997 and in the U.S. in 2001. Many more have since come out.
We're referring here to hybrid-electric vehicles (HEVs) that use combustion engines and electric motors (also called motor generators) in conjunction to yield better gas mileage than standard cars.
You still have to fill them up with gasoline, but the electric motor leads to gains in fuel efficiency by allowing the combustion engine to shut down while idling via automatic start/shutoff. It also provides additional power while the car is accelerating or going uphill through electric motor drive/assist, enabling installation of a smaller, more efficient gas engine. Some hybrids use regenerative braking. While the motor is applying resistance to the drive train and slowing the car, energy from the wheel is turning the motor and generating electricity, which is stored in the metal hydride (NiMH) battery for later use. Some of the more expensive hybrids can also operate in electric-only mode for a few miles, although others will shut down if they have no gas.
Depending upon make and model, hybrid-electric cars can get far better gas mileage than comparatively sized traditional vehicles.