Unfortunately, the high cost of premium gasoline may outweigh that advantage for many drivers. As a result, AAA recommends drivers weigh the potential benefits against the cost of using premium gasoline, if their vehicle does not require it.

AAA’s testing reveals that drivers could see modest gains in fuel economy and performance when opting for premium gasoline in vehicles that recommend, but do not require, the higher-octane fuel. Those seeking the maximum capabilities of their performance-focused or utility vehicle may see some benefit from using premium gasoline, particularly over the long haul.

—Megan McKernan, manager of the Automobile Club of Southern California’s Automotive Research Center

In partnership with the Automobile Club of Southern California’s Automotive Research Center, AAA tested a variety of vehicles that recommend, but do not require, the use of premium (91 octane or higher) gasoline. Although drivers of these vehicles are unlikely to see any benefit from using premium gasoline during typical city or highway driving, a combination of laboratory and on-road tests were performed to simulate extreme driving scenarios such as towing, hauling cargo and aggressive acceleration. When using premium fuel in these vehicles under these conditions, AAA tests found that:

• Fuel economy for test vehicles averaged a 2.7% improvement. Individual vehicle test result averages ranged from a decrease of 1% (2016 Audi A3) to an improvement of 7.1% (2016 Cadillac Escalade).

• Horsepower for test vehicles averaged an increase of 1.4%. Individual vehicle test result averages ranged from a decrease of 0.3% (2016 Jeep Renegade) to an improvement of 3.2% (2017 Ford Mustang).

• According to national averages, the price difference between regular and premium gasoline is approximately 20 to 25%, or 50 cents per gallon.

• The modest fuel economy improvements found in AAA tests do not offset the higher cost of premium gasoline.

Research that quantifies how a vehicle reacts to gasoline with different octane ratings is essentially looking at engine calibration – the programming done by the vehicle’s manufacturer to provide low emissions, high fuel economy, and maximum driving performance. Higher octane ratings are achieved by additives to gasoline that allow higher compression before the gas-air mixture in a combustion cylinder auto-ignites. This auto-ignition causes an audible knock or ping sound—particularly on hard acceleration or during a hill climb. Higher octane allows more power extraction before auto-ignition occurs, thus allowing an engine design that uses a higher compression ratio and or operating the engine with ignition timing further advanced. When the engine design and fuel requirements are closely matched, maximum operating efficiency can be obtained. For the consumer, this means better performance and fuel economy.

To complicate the engine calibration challenge, automakers cannot rigidly enforce the octane level and quality of gasoline used in the vehicles they produce. Fuel quality varies by region across the United States. Drivers can freely select from 85 octane regular to super-premium 94 octane (or higher) depending on the area of the country and fuel retailer. Knowing what octane gasoline is recommended or required by your vehicle can help maximize both fuel economy and performance.

—AAA Premium Fuel Research, Phase II

For those vehicles that do not recommend or require premium gasoline, AAA suggests drivers opt for the lower priced, regular fuel. In a study released last year, AAA found that consumers wasted nearly $2.1 billion dollars fueling these vehicles with higher-octane gasoline. However, drivers of vehicles that require premium gasoline should always use it. Additionally, any vehicle that makes a “pinging” or “knocking” sound while using regular gasoline should be evaluated by a repair facility and likely switched to a higher-octane fuel, AAA said.