CHICAGO -- Hopeful signs about the economy may tempt you to spring for premium when you pull up to the pumps these days.
Don't give in. Stay "regular."
Premium may sound like a way to pamper your vehicle and make it perform better or longer. But it's more often just a way to spend an extra few bucks a tankful when you don't have to.
"If your car can run on regular, just run it on regular," said David Champion, director of automobile testing for Consumer Reports. "By putting premium into a car that runs on regular, normally you will not improve its performance or fuel economy."
Here are some questions and answers about premium fuel.
Q: What exactly is premium gasoline?
A: A fuel with a high octane rating, which means it's less likely to cause your engine to knock or ping. Premium gas has an octane rating or anti-knock index of 91 or 92 in most of the U.S., compared with 88 to 90 for midgrade and 87 for regular.
Some higher-octane gas also may have cleansing additives or detergents, which ensure that the fuel lines don't get gunked up with deposits. But regular gas has gotten better over the years and generally keeps fuel injectors and intake valves clean. Most cars also have anti-knocking sensors which adjust to the type of gasoline.
Q: How much more does premium cost than regular?
A: Roughly a quarter extra per gallon -- more in some places -- or an additional $7 or so to fill up an SUV with a 30-gallon tank. The average nationwide price for a gallon of premium gas as of Monday was $2.88, according to the Energy Information Administration. That compared with $2.76 for midgrade and $2.64 for regular.
Q: Who should use it?
A: Use premium in any vehicle for which the manufacturer says it is required. Usually that's sports and luxury vehicles, which have high-performance engines that provide more horsepower but are vulnerable to knocking when high-octane fuel isn't used.
If nothing indicates "premium fuel only" in the owner's manual or on the gas cap, gas gauge or gas-tank door, use regular.
Even the American Petroleum Institute, the oil industry's trade association, advises going with whatever the owner's manual recommends.
Q: Who actually is using it?
A: Luxury vehicle owners are the biggest premium users, but some demand comes from drivers of other cars who believe it cleans out the engine or revs up the performance of older engines. The use of high-octane fuel is creeping back up after the combination of soaring prices and the recession drove it last year to its lowest point in 24 years.
Premium accounted for 9 percent of the nationwide fuel market share in May, the latest figures available from the Energy Information Administration. That was up slightly from a year earlier, though still well down from 17 percent in the same month a decade ago when the economy was booming and demand for premium was near a peak.
Q: What if the owner's manual recommends using premium for best performance?
A: You might give up some performance by using regular -- about 2 percent to 3 percent of your engine power, according to Consumer Reports. But it makes scant difference to fuel economy. Consumer Reports found that the temperature and humidity make more of a difference. In other words, it's probably better to save the cash and stick with regular.
Q: So premium fuel can sometimes help?
A: Yes, though not nearly as much as with older engines that were less dependent on electronic systems. American Petroleum Institute spokesman Prentiss Searles says it probably won't make a difference for most cars in everyday situations. But he suggests you might get better results when, for example, your car is pulling a heavy load up a hill.
Q: What if I am using regular and I hear pinging or knocking?
A: If the engine is pinging or running rough, try a midgrade fuel, then premium if it keeps up.
Q: Does the brand of gas make a difference in fuel selection?
A: Champion of Consumer Reports recommends always going to name-brand gas stations such as BP, Chevron, Exxon Mobil, Shell or Texaco rather than off-brand ones where the gas may be of less consistent quality.
Also, busy gas stations are likely to have cleaner fuel than those where traffic is light and the gas could collect dirt particles the longer it sits in underground tanks.
Q: How does altitude affect octane requirements?
A: Cars generally have lower octane needs at high altitudes. So in the Rocky Mountains and some other high-altitude areas, the octane ratings for gasoline grades may be two or more octane points lower.
Q: Is premium fuel cleaner than regular -- any better for the environment?
A: No, they're about the same. You need to drive less if you want to help the environment.