In a world where both climate predictions and gas prices seem increasingly volatile, many hope for greater fuel mileage and reduced greenhouse gas emissions through the use of “hybrid car” technology.

But what is a hybrid car, really? What factors distinguish them from the average auto-vehicles that one should be motivated to pay the extra?

While the media often takes the generalized term “hybrid car” and portrays it as a single type of vehicle, Auto-X-Prize team member Matt Robinson explained that, “all hybrids aren’t created equal.”

Though technically, any type of vehicle that uses two or more sources of energy is defined as a “hybrid car,” most of the currently available hybrids are hybrid-electric vehicles since they enjoy a competitive edge in the market.

For instance, they come with smaller battery packs than pure electric vehicle or hydraulic vehicles, reducing the cost and time of recharging, while the on-board gas tank provides a driving range comparable to conventional auto vehicles.

Hybrid electric vehicles can be broken down based on how the car uses the energy.

“Series” cars, like the Chevy Volt, have an electric motor with enough power to drive the wheel while the energy from gasoline could charge a battery, capacitor, or directly power the engine.

In “parallel” and “power split” hybrid vehicles, an engine and an electric motor share the work of driving the wheel. (The popular Honda Insight and Toyota Prius are parallel hybrid vehicles).

“Plug-in” vehicles, such as the Ford Escape plug-in hybrid, on the other hand, store energy in battery packs partially through plugging into an outlet. They often have an increased energy storage capacity by employing lithium-ion batteries.

In all types of electric vehicles, electrical energy is generally stored in the battery to power the electric motor, which then turns the wheels.

In a car run purely on gasoline, however, gasoline pumps the engine to turn the wheels.

Although it is true that the battery-motor process is much more efficient than that of gasoline-engine, this is not the main reason why hybrid cars are more efficient, as the process of storing energy into readily usable electricity to the battery pack is not very efficient.

Rather, hybrid electric cars shoot for greater efficiency by minimizing energy waste. Multiple hybrid cars, for instance, use regenerative brake systems that store the left-over energy to the battery pack when the car stops. Some show the real time gas mileage to the driver so he or she will be motivated to drive at an optimal speed.

Despite such efforts to improve efficiency, Prof. Max K. Zhang, mechanical and aerospace engineering, said that the money saved by the gas mileage of the hybrid car will not match the cost of premium unless one drives a lot and the price of gas is high.

Those that do pay the premium for hybrid car say that the money spent may help create momentum for this developing technology and, someday, for a healthier environment.