Choices at the Gas Pump Have Changed but Work the Same

Sept. 30, 2013

LINCOLN, Neb. — Choices have changed at the gas pump, but drivers shouldn't see a change in how fuel performs in their cars, a University of Nebraska-Lincoln Extension educator says.

Motorists for many years have had a choice of gasoline fuel with octane ratings of 87 regular, 89 with 10 percent ethanol or 91 premium. However, oil companies have started to run a sub-octane fuel up the pipeline, which is 83 or 84 octane, said John Hay, associate extension educator in biological systems engineering at UNL.

Mixing ethanol with the sub-octane fuel gives it the octane boost it needs to reach 87 octane level. Ethanol has an octane rating of 100. Fuel stations have begun to change their pumps and labels to reflect the new blends.

"This sub-octane fuel needs to be blended with other fuel types to make it the 87 octane level or above we need at the pump," Hay said. "So basically, 87 with ethanol replaced the 89 with ethanol, and our low cost option at the pump is now 87 with ethanol."

Hay said for those that used to fill up with 89 with ethanol, they can now fill up with 87 with ethanol and it will work the same in their engines.

Before the changes, Hay said there was about a 10-cent price difference in regular gas versus the 10 percent ethanol blend. However, since the changes, that has been ranging 15 to 25 cents across the state.

"The reason is because the 87 regular used to be just the fuel coming out of the pipeline; now it has to be blended with 91 octane premium fuel to make the 87 octane regular," Hay said.

The majority of the U.S. has already seen this change, and Hay said Midwest fuel stations will be deciding what blends to carry and what prices to charge over the next few months.

An octane rating ranks fuel's ability to compress without detonating.

"The average car needs a minimum octane rating of 87," Hay said, but be sure to consult your owner's manual for minimum octane required for your car.  "To take advantage of higher octanes, you need a car with higher compressions, such as a high-performance sports car."

Octane is not a rating of energy density and both the 87 with ethanol and the old 89 with ethanol have the similar Btu content and will both give drivers the same gas mileage.

Hay said another fuel fact is about winter and summer fuel.

As winter approaches, oil companies will begin their annual change to "winter" fuel. This winter fuel will have the same octane but is made of shorter chains of hydrocarbons and is thus more volatile and less energy dense.

The higher volatility helps with cold start in winter conditions, yet has less energy than summer blend gasoline. This reduction in Btu content will be accompanied by lower gas mileage but also a lower price at the pump, Hay said.

He said the oil market has a lot of price volatility and thus price changes due to switchovers like summer to winter and winter to summer are hard to notice. Similarly driving conditions and styles make fuel mileage fluctuate, making small changes in the fuels energy hard to distinguish.