Regular and premium gasoline differ primarily in octane rating, which measures resistance to engine knock. A higher number does not automatically mean more energy, better cleaning, or improved fuel economy.

According to the U.S. Department of Energy’s fuel-economy guidance, drivers should use the octane rating specified by their vehicle’s manufacturer*. Under normal driving conditions, using higher-octane gasoline than the engine needs may provide little to no performance or fuel-economy benefit.

Octane measures how well gasoline resists abnormal combustion, commonly called knock or pinging. Knock occurs when part of the air-fuel mixture ignites uncontrollably instead of burning as intended.

U.S. pumps display the Anti-Knock Index, or AKI, calculated as the average of the Research Octane Number and Motor Octane Number. You may see this written as “(R+M)/2” in your Chevrolet owner’s manual.

Higher cylinder pressures can increase an engine’s octane needs. That is why some high-compression, turbocharged, or supercharged engines call for premium. However, a turbocharger alone does not mean premium is required. The manufacturer’s calibration determines the appropriate fuel.

“Required” identifies a minimum fuel specification. “Recommended” may allow a lower grade under conditions explained in the owner’s manual. These terms are not interchangeable.

A premium-recommended engine may produce less power or deliver lower fuel economy when using an expressly permitted lower grade. That does not make regular acceptable in a different engine that requires premium.

Some Chevrolet performance engines require premium, while certain truck and SUV engines recommend it. Fuel requirements depend on the engine and vehicle generation, not just the model name. Use this table as a starting point, then confirm the instructions for your specific Chevrolet.

Some GM manuals recommend 93 octane, so a blanket instruction to use “91 or higher” can miss an important distinction. Find your vehicle’s instructions through Chevrolet’s official Manuals and Guides. Look for “Recommended Fuel” in the driving and operating section, and review any separate performance supplement that applies.

The result depends on whether premium is recommended or required. One accidental fill-up does not automatically mean engine damage, but using fuel below the required minimum should not be ignored:

• If Premium Is Recommended: If the manual explicitly permits regular, the vehicle may adjust engine operation to accommodate it. Reduced acceleration or fuel economy can result. Follow the manual’s restrictions, including any instructions related to heavy loads or performance driving.
• If Premium Is Required: Using lower-octane fuel can cause poor operation, knock, and potentially engine or emissions-system damage. Modern knock-control systems are not permission to disregard the required fuel grade.

Avoid hard acceleration and heavy loads while obtaining vehicle-specific guidance. If you hear persistent knocking, experience significant power loss, or see a flashing check-engine light, pull over safely and arrange assistance.

Putting diesel into a gasoline vehicle, gasoline into a diesel vehicle, or an unapproved ethanol blend into either is different from choosing the wrong octane. Do not start the engine if you realize the mistake before starting. Contact a qualified service professional for instructions. If the engine is already running, stop safely and request assistance rather than trying to use up the fuel.

Using a higher-octane gasoline that otherwise meets the vehicle’s fuel specifications generally does not harm an engine designed for regular. However, it usually offers little to no benefit during normal driving.

Premium is not a repair for rough running, poor fuel economy, or a check-engine light. If your Chevrolet develops those symptoms, diagnosing the cause is more useful than repeatedly switching grades.

Premium does not guarantee better MPG, and octane is not a measure of detergent quality. Engines designed to take advantage of higher octane may benefit, particularly under demanding conditions, but results vary. Keep these distinctions in mind:

• Higher octane improves resistance to knock rather than automatically increasing fuel energy.
• Detergent standards describe cleaning performance, which is separate from octane grade.
• Hot weather, towing, and heavy loads can increase operating demands, but they do not replace the fuel instructions in your manual.

For towing around Milton or summer travel through DeFuniak Springs, review both the fuel guidance and trailering instructions before departure.