In fact, a hybrid car t is a cross between a gasoline-powered car and an electric car. There are two kinds of hybrid cars. One way is a parallel hybrid. In this, a fuel tank supplies gasoline to the engine. But it also has a set of batteries that supplies power to an electric motor. Both the engine and the electric motor can turn the transmission at the same time, and the transmission then turns the wheels. As a result, in a parallel hybrid, both the electric motor and the gas engine can provide propulsion power. The other is a series hybrid. In this, the gasoline engine turns a generator, and the generator can either charge the batteries or power an electric motor that drives the transmission. Thus, the gasoline engine never directly powers the vehicle.

One might think the reasons for building such a complicated machine when most people are perfectly happy with their gasoline-powered cars. There are two reasons: first, there is pressure to reduce tailpipe emissions and to improve mileage....

As a car that burns twice as much gas to go a mile will generate approximately twice as much pollution. That pollution will have to be removed by the emissions control equipment on the car. So decreasing the fuel consumption of the car is one of the surest ways to decrease emissions.
The other reason is that gasoline driven cars emit too much of Carbon dioxide (CO2) that contributes to global warming. Since it is not regulated, a car has no devices for removing CO2 from the exhaust, so a car that burns twice as much gas adds twice as much CO2 to the atmosphere.

Finally, the increasing cost of the gasoline has put pressure on automakers for greener and healthier environment.