By Mike Ramsey and Doron Levin Jan. 15 (Bloomberg) — Bayerische Motoren Werke AG will sell a 7-series sedan in the U.S. with a six-cylinder engine for the first time in 18 years as the industry’s push for better fuel economy reaches the top end of the luxury category. Four-cylinder engines also will return in smaller models after a hiatus dating to 1999, Munich-based BMW said this week at the North American International Auto Show in Detroit. The shift is a response to the Obama administration’s 2009 mileage rules. For BMW, the world’s largest maker of luxury autos, the challenge in the 7-Series is convincing buyers that turbocharged six-cylinder engines will be close enough to V-8 performance to justify prices exceeding $70,000. “Downsizing the engines with boosting is what has to happen,” said Aaron Bragman , an analyst at IHS Global Insight Inc. in Troy, Michigan. “This is more about regulation than customers’ desire for fuel efficiency.” General Motors Co. and Hyundai Motor Co. also used the auto show to display new mid-sized cars with only four-cylinder engines to help meet the new mileage standards, which call for having average fuel economy of 35.5 miles per gallon by 2016. Keeping Horsepower Turbochargers, better transmissions and fuel-injection technology will help automakers maintain horsepower, said Chris Meagher, the chief engineer for Detroit-based GM’s Ecotec four- cylinder engines. BMW’s cars and light trucks averaged 27.5 mpg and 23.1 mpg in 2009, according to the National Highway Traffic Safety Administration . “We have heard customers asking for a wider range of options to balance individual demands and concerns for increased efficiency and lower CO2, and if they were going to stay with BMW they want the same performance they always expected,” said Jim O’Donnell , chief executive officer of BMW U.S. Holding Corp., which is based in Woodcliff Lake, New Jersey. Competitors for the 7-Series such as the A8 from Volkswagen AG ’s Audi and the S-Class from Daimler AG’s Mercedes-Benz don’t have gasoline-only six-cylinder options. Daimler sells a six- cylinder S-Class hybrid, according to the Mercedes-Benz Web site. BMW’s new 740i , which will start at $71,025 when it reaches dealers this year, will put out 315 horsepower with the aid of twin turbochargers, according to the company. That’s 44 percent more than the last six-cylinder 7-Series, a 735i sold in 1992. Top of Line The 7-Series is BMW’s top-of-the-line model in the U.S., according to the automaker’s Web site. The car will still be offered with V-8 and V-12 engines, BMW said. While the new 740i hasn’t been rated by the Environmental Protection Agency , its fuel economy will be more than a 10 percent improvement over the V-8 750i, which gets 22 mpg, according to BMW. BMW’s last four-cylinder U.S. car was a 3-Series in 1999. The smaller engine will return in new vehicles debuting in the next three years, Tom Kowaleski , a spokesman, said yesterday, while declining to specify the models. Acceptance of four-cylinder engines is growing. In 2009, 62 percent of all cars built for the U.S. market had such an engine, the highest share on record, according to researcher Paul Zajac at Ward’s Automotive Group in Southfield, Michigan. A new four-cylinder Sonata, Hyundai’s highest-volume U.S. model, went on display this week at the Detroit auto show. In its base configuration, it will turn out 198 horsepower and get 35 mpg on the highway, according to the Seoul-based company. The car arrives in showrooms next month. Hyundai, GM “The best way to cost-effectively improve our industry’s fuel economy right now isn’t through hybridization,” said Chris Hosford , a Hyundai spokesman. “It’s through the rapid introduction of four-cylinder engines.” GM’s Buick Regal , a new sedan due to go on sale this year, will only be offered with four-cylinder engines. A version with a turbocharged 2-liter engine will produce 220 horsepower, topping the 205 horsepower from the 5.7-liter V-8 in GM’s 1984 Chevrolet Corvette sports car, according to the company . “In the mid-sized segment, fuel economy is a key driver of consideration,” said Craig Bierley, product marketing director for Buick. “Being able to deliver a four-cylinder that could give very, very acceptable performance is important for us.” To contact the reporters on this story: Mike Ramsey in Detroit mramsey6@bloomberg.net ; Doron Levin in Detroit at dlevin5@bloomberg.net