The vast majority of the cars over on the road, 90+ percent of the vehicles on the road and do not require premium fuel. So it is worth understanding what makes premium gas more expensive and what drivers are actually getting out of it.
The primary trait that distinguishes premium gas from a lower grade and less expensive fuel is its octane rating. Understanding that octane reading and which cars are engineered for which gasoline is key to knowing whether it is worth ponying up for the pricier stuff.
There are typically three grades of fuel found at the gas pump in the United States, regular, mid-grade, sometimes called plus, and a third level, often called premium or something similar.
The way to distinguish these is by their octane ratings. The number that will be typically displayed on the button used to select the fuel grade. Regular has an octane rating of at least 87, mid-grade runs, 88 to 90, and premium 91 to 94.
In some higher elevation regions, 85 octane gas can be used in some cars and is often found at pumps.
In octane rating determines how resistant a fuel will be to combustion, which matters because engines require that gasoline explodes at exactly the right time. In an internal combustion engine, fuel and air combine inside a cylinder chamber, where they are compressed by a piston and then ignited by a spark plug.
The explosion pushes the piston, which turns a crankshaft and ultimately turns the wheels that move a vehicle. Everything needs to happen in that order, and the process happens extremely quickly because an engine consists of several cylinders, all connected to the same crankshaft.
Getting the timing right is crucial. If the octane rating is too low for a certain engine, the fuel and air mixture inside the cylinder can combust before the spark plug ignites it.
This phenomenon, a form of abnormal combustion, throws off the engine’s timing and can damage it, sometimes severely. This mistimed explosion can also create a knocking or pinging sound in the engine, which is why the phenomenon is often called engine knock.
So why would a fuel ignite before it is supposed to? Well, different engines have different compression ratios. That is the amount of pressure applied to the cylinder. An engine that can create more pressure can squeeze more energy out of every drop of fuel. Engines with high compression ratios are typically made for higher performance, whether it is large trucks used for towing big loads or race cars.
The preferred method for preventing knock was once adding led to gasoline. The element had antilock properties, but the Clean Air Act in the 1970s banned the use of lead in the United States.
Notice that all gasoline in the U.S. is referred to as unleaded. So the industry had to find other chemicals to reduce knocking. Today, two primary sources are used alkylate, a chemical byproduct of petroleum refining, and ethanol – basically, an alcohol derived from plants.
Cars with very high-performance engines require very high octane fuel. Some fueling stations, usually near racetracks, can have dedicated pumps with octane fuel rated at 100 or above. But most engines on the roads simply don’t need that because they don’t create enough pressure to require it.
And for many cars, there is little, if any, the benefit to putting high-grade fuel in an ordinary engine. The higher price of premium gas and the marketing around it appears to be part of its appeal for some drivers, the very fact that it is called premium or some synonymous name like supreme suggests fuel of a higher quality.
The labeling is certainly something to consider. You put a premium on something, and people will assume that it is a premium product. The vehicle is the second-largest asset that we have. There are a lot of people that believe that they want to take care of that asset by doing the best thing possible for it. But you’re literally putting that money out of the tailpipe when you make that decision.
There also appears to be a common perception that premium gasoline somehow contains extra ingredients that help clean engines or make them run more smoothly.
There are certain additives required by the Environmental Protection Agency, included in all gasoline, and some retailers have added extra additive on top of that. A group of automakers banded together and developed a Top Tier gasoline standard with extra detergents that remove more buildup than the lowest permissible standard.
Tests performed by the American Automobile Association, more commonly known as AAA, found that the Top Tier standard can keep engines up to 19 times cleaner. Top Tier gasoline is offered only by some retailers, but in order to qualify as a Top Tier provider, a retailer has to provide these extra additives in all fuel grades.
Additives or not, AAA and other industry groups say owners should use the grade of fuel the manufacturer says they should use. Some manuals say regular gas is fine. Others might allow regular but recommend premium. And a relatively small portion of cars requires a premium.
If a vehicle manual says regular gasoline is fine, then adding a premium is not going to make much of a difference.
The biggest myth is that premium is somehow much better, or you can get some sort of performance increase from premium. But this really goes back to what your car manufacturer intended your car to be used for. That is unless you drive a vehicle that requires higher octane fuel and can be damaged if you try to substitute something lower.
This is where things become a bit nuanced. Over the last decade or so, automakers have increasingly relied on a long available technology called forced induction to make engines run more powerfully or efficiently. Two very common forms of forced induction systems are turbochargers and superchargers. Essentially, these systems compress and force air into the engine.
Since an engine works by igniting a mixture of air and fuel, forcing more air into a cylinder along with an increase in fuel allows each engine cylinder to get more power than it otherwise would if it were naturally aspirated.
That is, if the engine simply sucked in air from the atmosphere. Turbochargers have become a popular choice for automakers looking to squeeze more power out of a smaller engine, often improving miles per gallon and meeting increasingly stringent fuel economy regulations.
In 2008, just 10 percent of cars came standard with turbocharged engines. By 2018, that number had climbed to 45 percent. The rub is that forced induction creates greater pressure in the engine and thus may either require or benefit from higher octane, i.e., more expensive fuel.
That said, even driving a turbocharged vehicle does not guarantee you need high octane fuel, and a naturally aspirated high-performance vehicle may require it. Automakers now place systems in vehicles that can sense knocking or pinging vibrations and adjust sparkplug timing to work better with the fuel in the tank.
There are certain situations where premium gas might confer an advantage, such as when towing or carrying a heavy load. However, even in that case, AAA tests have shown the performance difference is very, very small, somewhere around three to five percent in terms of economy or horsepower.
Higher octane fuel has always been more expensive than regular, but in recent years, the price gap between regular and premium fuel has widened dramatically. And it is worse in different parts of the country. And in different areas of the country, the premium between regular and premium, the gap between regular grade and premium grade is much higher, especially in areas of the Great Lakes.
On average, across the United States, the premium is about 50 to 60 cents higher per gallon. But the gap between premium and regular is especially wide in areas like the Great Lakes region.
Now for premium, you may find 50 to 60 cents common for a national average of that premium as more. And it wasn’t always like that. The reason for this gap is the availability of the alkylate used to ramp up octane levels in the fuel. Regions like the West Coast, where there is a higher demand for premium fuel, have induced refiners to build more alkylate capacity into the refining processes.
But areas such as the Great Lakes, where there is not as much demand for high octane fuel, have a lesser capacity to produce the stuff. However, the gap is widening everywhere. AAA tracking has found that the price gap between premium and regular tends to widen when overall fuel prices drop and narrow when fuel prices climb.
New fuel blends may help raise octane levels in cars at a lower cost, and one of them may include something you typically see on your dinner plate – corn. Ethanol, which is chemically alcohol, is refined from vegetables. And in the United States, that typically means corn. Ethanol has the benefit of being a very high octane substance.
Many cars on the road can run on fuels that are up to 85 percent ethanol, typically referred to as flex-fuel vehicles. They first garnered attention as a solution to reducing greenhouse gases. Flex-fuel vehicles get comparable power and acceleration to gasoline-only vehicles, though they tend to get fewer miles per gallon.
Data suggest E85 emits lower concentrations of some greenhouse gases but higher concentrations of other toxins. Part of what makes ethanol gas a carbon-reducing solution is the fact that it is made from crops, which act as a sink for the carbon dioxide released into the atmosphere by the burning of fuels.
And it is possible that his car companies make internal combustion engines ever more efficient, in part to meet emissions regulations. They could design ordinary engines in ways race car engines are designed today.
One of the biggest stories in the automotive world over the last two decades has been the slow but determined shift toward electric cars. And for many drivers, trips to the gas station are already a thing of the past. But electric vehicles in 2020 still make up less than two percent of sales.
And many in the industry say the bridge to a fully electric fleet could take a long, long time. So in the meantime, the millions of drivers that pack roads across the country will have to keep filling up. A staggering number of them could find one of the biggest ways to save money. Doing so is printed in plain English right in their own vehicle’s manual.