GENEVA -- German carmakers are bringing gasoline direct injection technology to the United States.

Audi hit the market first and will be followed closely by BMW. But Mercedes-Benz will wait for wider availability of low-sulfur fuel.

Gasoline direct injection systems improve combustion by spraying fuel directly into the combustion chamber instead of into a port in the cylinder head, which is the system used in most gasoline-powered cars.

German carmakers are optimistic that the technology will boost fuel economy. One expert estimates that a 15 percent fuel-economy gain would make the technology viable.

Audi offers direct injection on these models sold in America: A3, A4, A6, A8 and Q7. "The goal is to switch to direct injection across the entire lineup," said Audi spokesman Josef Schlossmacher.

BMW will launch gasoline direct injection in Europe next month in the 3-series coupe. BMW will debut it in North America later this year. BMW showed a 3.0-liter, twin-turbocharged V-6 with gasoline direct injection at the Geneva auto show. "We will deliver this engine worldwide," said Klaus Borgmann, director of powertrain development for BMW in Munich.

But the CLS 350 CGI that Mercedes-Benz showed at Geneva won't go on sale yet in the United States because fuels there don't have consistently low sulfur content, company officials said. Extra sulfur creates noxious emissions.

The Pontiac Solstice GXP, due this August, will be the first car from a U.S. automaker with gasoline direct injection.

Tom Bauer, business development manager for Siemens VDO's powertrain gasoline systems group in Newport News, Va., said direct injection offers "three things - fuel economy, emissions and power or torque." Siemens supplies direct injection systems for several automakers, including Audi and BMW.

Juergen Gerhhardt, a Robert Bosch AG senior vice president in Stuttgart, said about 1 million vehicles with gasoline direct injection were produced worldwide in 2005. That will triple by 2010, he predicted. Bosch is the largest supplier of direct injection systems. It made the system on the Mercedes CLS shown at Geneva.

Richard Parry-Jones, Ford Motor Co.'s global chief technical officer, said gasoline direct injection has to achieve a 15 percent improvement over current gas engines to make economic sense.

But Parry-Jones is optimistic: "We're at a tipping point. I think it (gasoline direct injection) will increasingly be deployed."