Automakers are fully behind the Obama administration's new set of fuel-economy rules unveiled Tuesday. But make no mistake — these regulations will not be easy for them to meet.

Automakers are fully behind the Obama administration's new set of fuel-economy rules unveiled Tuesday. But make no mistake — these regulations will not be easy for them to meet.

The new rules call for manufacturers to reach an overall fleet average of 35.5 mpg by 2016, with passenger cars reaching 39 mpg and light trucks hitting 30 mpg under a system that develops standards for each vehicle class size. Manufacturers also would be required to hit individual mileage targets.

The regulations are expected to cut American oil use by billions of barrels, which is equivalent to removing hundreds of millions of cars from U.S. roads. But they are expected to cost car buyers an extra $1,300 per vehicle by the time the plan is complete.

They also will have a cost for automakers, who will have to pour billions more dollars into new technologies to help them meet those goals. The Transportation Department last year estimated that requiring the industry to meet a looser standard of 31.6 mpg by 2015 would cost nearly $47 billion.

Here are some questions and answers about what the automakers will need to do to achieve the new standards for emissions and fuel economy.

Q: How big a challenge will this be for the industry?

A: To get an idea for how far away the auto industry is from the new benchmarks, consider this: Only six vehicles on sale today offer fuel economy of at least 35.5 mpg, according to the auto Web site Edmunds.com. They are the Toyota Prius, the Honda Insight, the Honda Civic hybrid, the Ford Fusion hybrid, the Mercury Milan hybrid and the Smart fortwo microcar.

Q: So what are they going to do to meet these requirements?

A: For starters, manufacturer's have vehicles in the pipeline that will help them clear the new hurdles, and they will likely be announcing more.

Ford is bringing fuel-efficient small cars like the Fiesta to North America in the coming years and is planning on putting fully electric cars in showrooms by 2011. General Motors Corp. still plans to debut its Chevrolet Volt plug-in electric car next year — provided it isn't derailed by bankruptcy.

Chrysler LLC also has plans to introduce its own electric cars and small cars from Italian automaker Fiat Group SpA. Toyota and Honda will also be ramping up hybrid and plug-in vehicle production in the coming years.

Q: Are there other technologies that will help automakers meet the new regulations?

A: Besides more conventional hybrids and extended-range plug-ins like the Volt, expect to see so-called clean diesel cars like the Volkswagen Jetta TDI.

Extended-range plug-ins rely on a rechargeable battery for short distances, then a combination of gas and electric power for longer trips. Clean diesels use technology that filters out particulate matter and offers better fuel economy.

Automakers are also planning to introduce more exclusively electric vehicles. Meanwhile, companies like GM and Honda have long been experimenting with hydrogen fuel-cell vehicles, though they remain a long way off.

"There's all kinds of technologies that can be brought" to market, said Aaron Bragman, an auto analyst with the consulting firm IHS-Global Insight.

Q: When assessing a manufacturer's fuel economy rating, how will miles per gallon be calculated for vehicles like plug-in hybrids, which can be driven without using a drop of fuel as long as they don't travel too far at a time?

A: That isn't yet known. The EPA has said it is working on how to measure the fuel economy for these sorts of vehicles, and for pure electric cars and vehicles with other exotic powertrains.

Q: Could there be some unintended side effects of the new policy, in terms of what the manufacturers produce and sell?

A: U.S. automakers have long been criticized for relying too much on trucks and sport utility vehicles. And Jeremy Anwyl, chief executive of Edmunds.com, said the new rules might not change that because the fuel-economy standard for light trucks remains lower than the one for cars.

"In the United States, trucks have been sort of given a free pass on the (fuel-economy) standard," Anwyl said. "What's been happening is the automakers are building more and more vehicles and labeling them as light trucks."

As for cars, one easy way to boost fuel economy is to make them smaller. But that could raise questions about vehicle safety, Anwyl said.