The difference comes with the powertrain's mating to the 36-volt electric motor/generator, which forms the brawn of the GM Hybrid System.

The system allows the engine to shut off while stopped to minimize idling.  The engine automatically restarts when the driver lets off the brake pedal.  While the process involves no participation from the driver, it is sometimes disconcerting to feel the motor shutting down as you stop at a light.  I'm sure it is something that you get used to, but it does give the sensation that the car is stalling at times.

The system also allows early fuel shut-off during deceleration and captures kinetic energy through a regenerative braking system that charges the nickel metal hydride battery.  The electric motor provides additional power during launch, when needed, or at wide-open throttle, such as when passing.

The GM Hybrid system is designed to automatically maintain full accessory functionality when the vehicle is stopped, including climate control.  The A/C system allows a choice of two settings, though.  The first favors a more fuel-efficient performance by limiting the draw on the hybrid powertrain, while the normal mode provides maximum passenger comfort in hot climates and enhances defogging performance.

The cumulative affect of all of this technology is to improve fuel economy by two miles per gallon, boosting the 22 city/30 highway ratings to 24 city/32 highway.  The cost in performance is not really noticeable because of the assistance provided by the electric motor.  Top horsepower drops from 169 to 164, while top torque drops just one pound-foot from 160 to 159.

While the cost in performance would be hard to notice, the purchase price of $24,545 MSRP is almost $4,000 higher than the $20,550 of the base model Malibu LS.

With gas hovering at $4 a gallon and looking to be headed higher, this may begin to look like a bargain when you do the math.  That $4,000 would buy you 1,000 gallons of gas, which will carry you between 22,000 to 30,000 miles, suggesting that you will have made up the extra expense of buying the hybrid option fairly early in the car's lifecycle.