The German luxury trio of Mercedes-Benz, BMW and Audi are all locked in a close battle for the title of the world's most popular automaker. According to sales figures from the first half of 2010, BMW is currently in first place, although its lead over its two rivals is marginal. At under 2,000 vehicles, Mercedes' lead over third-place Audi is even slimmer, although that number may have grown in recent months thanks to strong sales for Mercedes in the U.S.

Regardless, all three German luxury brands are racing for the top spot. To accomplish this, they're going after smaller market segments. According to the Automotive News, the next segment that the brands are looking to cater to is the "green," or environmentally conscious, car owner.

Mercedes recently announced that it will debut a four-cylinder engine on its top-of-the-line S-Class model. The S250 CDI is expected to be available on several models in early 2011. Four-cylinders are uncommon options for luxury vehicles, with drivers typically wanting the performance of a six- or eight-cylinder. Yet Mercedes says that thanks to turbocharging technology, the engine delivers the torque of a six-cylinder with the low emissions and fuel consumption of smaller engines.

"Green luxury is feasible," said Verena Mueller, a Mercedes spokeswoman. "We expect to attract environmentally conscious customers who are seeking the lowest possible CO2 emissions. Besides private customers, that could of course also be fleet buyers."

The news source reports that Audi will counter with a new version of its A8 sedan that will likely see the automaker couple the four-cylinder with an electric motor for the A8 hybrid, which is expected in 2012.

BMW is also going the electric route, but is unlikely to make the move to a four-cylinder anytime soon. BMW is said to be developing a hybrid supercar based off of its Vision Efficient Dynamics concept.

"I like selling 7-series cars with six- and eight- cylinders," BMW CEO Norbert Reithofer told the news source at the Paris Motor Show. "What we need to offer with these cars in the future is electrification."

Smaller engines and electric vehicles might save drivers at the pump, but luxury cars outfitted with the latest in engine technology will likely be expensive for many buyers. Drivers interested in saving money on their vehicle purchase may want to shop for a used Mercedes, BMW or Audi.