We first saw GM’s new-generation of ‘eAssist’ mild-hybrid technology in the 2012 Buick LaCrosse, where it is equipped as a standard feature on the base four-cylinder LaCrosse. Today GM is announcing that the 2012 Buick Regal will also come with eAssist, though it will be offered as an option.

eAssist essentially pairs a small electric motor with the Regal’s 182 horsepower 2.4-liter four-cylinder engine and six-speed automatic gearbox to boost acceleration during high load situations and help reduce fuel consumption. The electric motor also acts as the car’s alternator-generator, topping up the batteries when needed and running ancillary features like the air conditioner. The system also features a regenerative braking system to help charge the car’s air-cooled 115 volt lithium battery pack.

Unlike a full hybrid system, eAssist cannot power a vehicle on electric power alone. Not surprisingly, the electric motor only adds about 15 horsepower during high load situations and the system can generate up to 20 horsepower from its regenerative brakes. eAssist can, however, shut down the vehicle’s engine when stationary or when coasting to a stop and almost instantly restart it once the accelerator pedal is depressed.

2012 Buick Regal with eAssist

2012 Buick Regal with eAssist

According to GM, the technology improves overall fuel economy in the standard four-cylinder Regal by about 25 percent, returning an estimated 26 mpg city and 37 mpg on the highway.

The new 2012 Buick Regal with eAssist will go on sale this fall, following its debut tomorrow at the 2011 Chicago Auto Show. In the meantime, you can follow our complete coverage of the show by clicking here.

For more details, check out John Voelcker extensive report over at GreenCarReports.