Once upon a time, the choice of what gasoline to put in your gas tank was relatively easy. Not any more.
Today, consumers are faced with economic pressures, ecological concerns and slick slogans that can leave car owners confused at the pump.
Consumer advocates suggest starting with octane ratings.
As many as 30 percent of car owners nationwide are paying an additional $3 billion a year for extra-octane gas they don't need, says Clarence Ditlow, director of the Center for Auto Safety in Washington.
Octane measures a gasoline's ability to burn evenly and not produce a knocking sound in an engine. Car owners should check their owner's manual to find what level is appropriate for their car, he says.
He warns consumers against overspending on gasoline that promises to pump up a car's performance with extra octane.
Using a gasoline of higher octane than a car needs will not increase performance or power, because a car's timing and other engine mechanisms are set by the manufacturer to burn a particular fuel. These components will not adjust by simply changing to a higher-octane gasoline.
"A lot of people will put premium gas in their car thinking it will make their car run better," says Bob Hoffman, service manager at Pacific Ford in Long Beach, Calif. "But the truth is, the computer in the car doesn't know what octane you're putting in it."
So why do consumers overspend on octane? Part of the reason may be the marketing strategies used by oil companies, says Gregg Fisher, assistant director of the General Accounting Office in Washington.
"There is some slick advertising out there," he says. Slogans such as "drive your engine clean" and "put a tiger in your engine" persuade consumers to spend big bucks, he says.
The GAO says the number of cars on American highways that depend on higher octane declined by nearly 20 percent from 1971 to 1988.