(AOL Autos) -- The little two-passenger smart fortwo is the most fuel-efficient car (not counting hybrids) in the U.S. market, with EPA fuel economy ratings of 33 mpg city, 41 highway. For high-mileage frugality, it appears to beat the five-passenger Toyota Yaris and its 29/35-mpg ratings by a long shot.



Look at the inside of your car's fuel door to find out whether you're required to use a certain octane gasoline.



But wait! Premium fuel -- which cost about 12 percent more than regular at U.S. pumps last month -- is required for the fortwo. Suddenly the gap closes and the Smart no longer looks like as strong of a fuel-budget buster. And with the requirement, they mean it: smart says you'll lose your warranty coverage if you don't ante up.



With premium fuel averaging about 24 cents more per gallon than regular, your choices at the pump can add up very quickly. If you drive a 20-mpg vehicle 15,000 miles a year, that's an extra $180, each year, toward those extra few octane points. If you have a thirstier truck or SUV or cover more mileage, it could amount to hundreds of dollars a year.



New-car buyers, take notice. Add fuel requirements to your shopping checklist, because it will impact your wallet with every visit to the gas station, for years of ownership.



The expensive stuff is typically recommended -- though not always required -- for luxury and high-performance cars, while less-expensive sedans, coupes, and SUVs only require 87-octane. But there are plenty of exceptions.



Alan Hall, a spokesman for Ford, says that the automaker no longer has any models that require premium grade and only a few for which it's recommended. Regular unleaded is fine across all the models of Ford's Lincoln  luxury brand, says Hall, so "as a luxury car buyer you don't have that added premium of premium fuel."



Ford now does all of its engine development and vehicle testing on 87-octane, regular-grade fuel. "We don't want to give you a product that will have durability issues," explains Hall, if premium-grade isn't available everywhere.



Another exception in the luxury-car realm is Hyundai; the automaker chose to tune the new high-performance V-8 engine in its Genesis sedan for premium fuel, but it also certified it for regular-grade.



The automaker is the first to list power figures both with premium (375 hp) and regular (368 hp), letting owners opt for either top performance or a substantial savings at the pump. For the record, there's no measurable difference in fuel economy between the two grades, or any greater potential for damage, according to Hyundai.



"We wanted to give customers the choice," explained Hyundai spokesman Miles Johnson. "If you want a few extra horsepower, go ahead and spend a little more at the pump."



Along with several European automakers, the BMW Group recommends premium fuel for all of its vehicles -- including the economical MINI Cooper -- yet Ford doesn't even recommend premium for its sporty, V-8-powered Mustang GT. The high-performance, 540-hp Shelby GT500 is the only new Ford vehicle to carry the recommendation for premium ... and Hall concedes the engine will get a "slight boost" from premium.



Throwing money away?



You might have been led to believe at some point that your vehicle will do better with premium, but with most newer vehicles, that's simply not true. Provided yours just calls for 87-octane, chances are you won't notice the difference, according to a number of experts, and you're essentially throwing the money away.



The best way to tell, advises John Nielsen, director of AAA's Auto Repair and Buying Network, is to simply look at the inside of the fuel door; if it says, "use premium fuel only," and specifies a higher octane number (regular is typically 87, premium is 91 or higher), then the expensive stuff is actually required for the
What can be found on inside of car's fuel door? What does Ford say? What caused Ford to start testing with regular grade fuel?
of your the automaker no longer has any models that require premium grade premium-grade isn't available everywhere.
question: What can be found on inside of car's fuel door?, answer: of your | question: What does Ford say?, answer: the automaker no longer has any models that require premium grade | question: What caused Ford to start testing with regular grade fuel?, answer: premium-grade isn't available everywhere.