Midgrade vs Regular Gas: What Is the Difference and Which Should You Buy?

Octane explained in plain terms, the price gap between 87 and 89, and a simple rule for choosing the right grade.

Updated November 3, 2026

At most U.S. stations you choose between three grades: regular (87), midgrade (89) and premium (91–93). The numbers are octane ratings, not measures of energy or cleanliness.

What octane actually means

Octane measures how well fuel resists knocking – premature ignition of the fuel-air mixture under compression. Engines with high compression or turbochargers need higher octane; engines designed for 87 do not. All three grades contain roughly the same energy per gallon and must include the same minimum detergent additives.

Side by side

The simple rule

1. Look at the owner’s manual or the label inside the fuel door.
2. Buy the octane it lists as required – no lower, and no higher.
3. If it says “recommended” for a higher grade, regular is safe; the higher grade may add a little power.

Exceptions

• Towing or carrying heavy loads in hot weather can make some engines knock on 87; if yours does and the manual allows it, 89 can help.
• High altitude: in mountain states, “regular” may be 85 octane. Modern fuel-injected cars may need 87 even there – check the manual.
• Older vehicles with carbon buildup sometimes knock on regular; a service visit is usually a better fix than paying more at every fill-up.

Bottom line

If your car is designed for regular, midgrade costs about $9 more per tank for no gain. Over a year of driving that can easily add up to $300 or more.

Frequently asked questions