Don't Confuse Gasoline Octane And Quality

AAA Auto Repair Article
By AAA Automotive
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If the manufacturer of your car recommends regular grade gasoline, you may wonder if premium will provide added benefits. On the other hand, if the automaker says premium gasoline is "recommended" or "required," you may have considered filling up with regular to save 30 to 50 cents-per-gallon. Do either of these options make sense and, more importantly, could they cause any problems? To help answer these questions, let’s talk about gasoline octane and quality.

Gasoline Octane

The key difference between regular and premium gasoline is octane – the ability of the fuel to prevent engine detonation or "knock." Uncontrolled knocking can cause severe engine damage and expensive repairs. Premium gasoline typically has an octane number four to six points higher than regular – 93 versus 87 for example.

Best Gasoline
Contrary to popular belief, premium grade fuel does not contain more power than regular. The energy content of premium gasoline is actually a little lower than that of regular due to its additional anti-knock additives.

The belief that high-octane fuel offers more power came about because automakers require premium gasoline in high-performance engines. However, it is not the fuel that provides the added power, but the engine's "state-of-tune," which involves a number of mechanical design factors. When these elements are optimized to produce more power, the possibility of engine knock increases, and with it the need for premium fuel to prevent engine damage and an expensive auto repair bill.

Gasoline Quality

All regular grade gasolines in any given area use the same base fuel, as do all premium grade gasolines. The only differences between fuel brands is the "secret sauce" of additives that are blended with the base fuel. These additives serve many purposes, but a major one is the prevention of carbon deposits inside the engine. These deposits reduce performance and fuel economy, and can lead to cold-starting issues and other driveability problems.

Since 1995, the Environmental Protection Agency (EPA) has required a minimum level of deposit control additives in gasoline. However, eight major automakers felt the EPA didn’t go far enough to keep engines running cleanly. In 2004, they released a TOP TIER (TM) gasoline standard that provides superior deposit control by requiring more and better additives. TOP TIER certification also mandates that the enhanced additives be used in all grades of fuel marketed by a company, and that those fuels be sold at all of the company’s retail locations in the U.S. and Canada.

Gasoline Recommendations

Regardless of whether your car calls for regular or premium, the best choice for ongoing performance and economy is a TOP TIER gasoline. Recent AAA testing found TOP TIER gasolines keep internal engine components up to 19 times cleaner than gasolines that only meet minimum EPA standards. The TOP TIER requirements are voluntary, but 63 fuel brands have signed on as of June 14, 2018.

If you drive a car whose manufacturer recommends regular gasoline, paying more for premium is a waste of money. Recent AAA testing found no increase in power or fuel economy, and no reduction in exhaust emissions, when premium gasoline was used in cars designed for regular.

If you drive a car whose manufacturer says premium gasoline is "recommended", you may be able to use regular gasoline with no problems other than small losses in power and fuel economy. A mid-grade gasoline can be used to balance the tradeoffs between premium and regular.

If you drive a car whose manufacturer says premium gasoline is "required", and particularly if it is a high-performance car often operated at high-rpm and high-loads, the greater anti-knock capability of premium gas is essential to prevent knocking and provide the maximum rated power output. This is particularly true of engines fitted with turbochargers or superchargers.

Here's the bottom line. If your premium-fuel engine runs fine on regular, you never hear any knocking, and the power it produces is acceptable, your car is unlikely to suffer any problems. However, any time you hear engine knock when using a lower grade of gasoline than that recommended by your vehicle’s manufacturer, you need to step up to a higher-octane fuel. Failure to do so will save you pennies now, but may later cost you hundreds or even thousands of dollars in auto repairs if engine damage occurs. It is also important to read your owner’s manual; on some cars the use of regular gasoline where premium is required can void the vehicle warranty.

Finding Quality Auto Repair

AAA recommends that you plan ahead for vehicle service by finding an auto repair shop and technician you can trust before you need them. provides information on nearly 7,000 Approved Auto Repair facilities that have met AAA’s high standards for appearance, technician training and certification, insurance coverage and customer satisfaction. AAA regularly inspects every Approved Auto Repair facility and surveys their customers to ensure ongoing performance. In addition, AAA members receive special benefits that include auto repair discounts, an extended 24-month/24,000-mile parts and labor warranty, and AAA assistance in resolving repair-related issues.
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