When Tracy Jackowski fills up her car, she pays no mind to the octane rating. The number that matters to her is the price.
"I use the cheapest gas there is," the Sylvania, Ohio, woman said as she pumped Valero regular grade into her Chevrolet Malibu. "I don't have a premium car. There's not that much difference, I don't think."
The experts would tell her she's right. Most people don't need to pay the extra 20 to 30 cents a gallon for high grade.
Premium gas is like coffee with a shot of espresso. It's basically the same thing, just brewed with some extra potency.
In engines designed for it, higher-octane fuel does deliver more power and can even help increase efficiency. But most cars aren't engineered to pull that extra juice out of the high-test.
"For 99 percent of the people, if your car says run on regular fuel, you're not going to see any benefit running on premium," said Roger Clark, the manager of General Motors Co.'s Energy Center.
Mr. Clark said it's important to check your vehicle's owner's manual to see what fuel the manufacturer recommends. If premium is required, you should follow the guideline. If it's only recommended, you're generally safe to fill up with whatever you want.
The grade of gas is set by its octane level. Essentially, the octane rating is a measure of the fuel's ability to resist knocking, or premature ignition in a cylinder. Typically, regular gas has an octane rating of 87, while premium is 91 or higher. Generally, higher compression engines call for higher octane fuel. Most gas stations sell three or four levels of fuel.
Manufacturers recommend mid-grade fuel for a handful of vehicles.
Across the market, about 17 percent of 2013 models require premium gas, according to data compiled by the automotive site Edmunds.com. Most of those are luxury or sports cars.
At GM, premium is only required in a handful of vehicles, most of which are high-end, high-performance machines such as the Corvette Z06 and the Cadillac CTS-V.
However, some luxury-oriented manufacturers such as BMW require premium across their lineups.
Keith Wallace, the service and parts manager at Yark BMW, said drivers should follow that guideline. "The long and short of it, if the manufacturer says premium, you should use it. Nobody should go against what the manufacturer tells you," he said.
Edmunds also says consumers should heed the advice of manufacturers who require premium in their cars.
However, experts agree that if your car doesn't require a premium diet, there's no real need to feed it the petroleum equivalent of steak when hamburger will do.
"Really what this boils down to for most people is they can probably go to the lower grade of gasoline, save quite a bit of money, not damage their car, and not notice a drop-off in performance," said Phil Reed, senior consumer advice editor with Edmunds.
Some manufacturers do recommend -- but not require -- premium fuel for certain cars, but Mr. Reed said it's unlikely most drivers will notice much performance difference by using it. Edmunds says premium is recommended for about 12 percent of 2013 model year cars.
Some people feel they're treating their car by giving it an occasional tank of premium, believing it's better for the engine and helps prolong engine life by cleaning out carbon deposits. Years ago, premium gas really was better, with additives and detergents not found in regular fuel. Nowadays, Mr. Reed said, every grade of gasoline has detergents and is of essentially the same quality.
That might explain part of the reason demand for premium gasoline has been falling in the United States.
Deliveries of premium fuel peaked in June 1988, at 85,343 gallons per day, according to the U.S. Energy Information Administration. Demand has fallen fairly consistently since then, especially since the late 1990s.
Block News Alliance consists of the Pittsburgh Post-Gazette and The Blade of Toledo, Ohio. Tyrel Linkhorn: email@example.com or 419-724-6134.