Improved efficiency is the story with BMW's new 3-series

BMW celebrated a big year in the U.S. market by introducing the sixth generation of its bread-and-butter model, the 3-series.

The automaker showed off two new versions of the 3-series, BMW’s best-selling model, in the U.S. and the rest of the world at the Detroit Auto Show.

First was the 335i, dressed up with the M Sport trim, followed by the ActiveHybrid 3, which combines a 335-horsepower six cylinder with an electric motor to deliver up to 37 miles per gallon highway.

BMW is also making fuel efficiency a priority in other 3-series models. For the first time in nearly two decades, the base 3-series, the 328i, will be powered by a four-cylinder engine. The turbocharged 240-horsepower 2.0-liter  engine replaces a 3.0-liter straight six in the current car. The top engine from the current car, a turbocharged version of the 3.0-liter six, will continue as the engine in the top 335i.

The automaker also emphasized the ability to customize its cars, a familiar theme at the 2012 North American International Auto Show. Besides the two engines, buyers can opt for three other packages:

• The Sport line builds on the base car’s sporty nature.
• The Luxury line adds refinement.
• The Modern line uses natural materials in the interior.

“These elements are the spirit of the Ultimate Driving Machine and they are in every one of our vehicles,” BMW Board Member Ian Robertson said.

BMW Board Member Klaus Draeger also emphasized a few key features of the hybrid. For one, he said the navigation system is integrated with the hybrid system to allow the car to move on electric power alone for the last half mile or so of the trip.

The new 3-series is expected to go on sale in February.

 Photos: 2012 BMW 3 series

Photos: 2012 BMW ActiveHybrid 5

Video: 2012 BMW 3-series