What is the gasoline octane rating in the United States?
3 Answers
The United States uses the Motor Method for gasoline octane ratings. Below is relevant information about gasoline octane ratings: 1. Three grades: According to data from the U.S. Department of Energy's Energy Information Administration, gasoline in the U.S., whether conventional, oxygenated, or otherwise reformulated, is divided into three grades: Regular, Midgrade, and Premium. Gas stations and the general public often refer to Midgrade gasoline as "Plus." These three grades nominally represent octane ratings of 85-88, 88-90, and over 90, respectively. In the Washington area, the three grades are 87, 89, and 93. 2. Research Method: China and European countries use the Research Octane Number (RON) to measure gasoline's anti-knock performance, commonly known as the octane rating. This method tests gasoline's anti-knock performance under engine speeds of 600 revolutions per minute and medium to low loads. Isooctane is used as the standard for anti-knock performance. If the tested fuel has the same anti-knock performance as a research gasoline containing 92% isooctane, the fuel is said to have a nominal octane rating of 92, and its grade is labeled as 92.
I remember being confused by these numbers when I first started refueling in the U.S. American gasoline grades are displayed as numbers like 87, 89, and 91 on the fuel pumps, representing octane ratings. 87 is Regular gasoline, which is sufficient for most standard vehicles; 89 is Mid-Grade; and 91 or 93 is Premium. You should check your car's owner's manual to determine which grade to use—my old Honda only needs 87. Don't assume that a higher number means better quality; what matters is whether your car requires it. Higher octane primarily improves knock resistance, which is why performance cars or turbocharged vehicles genuinely need 91. Gasoline grades may vary slightly (by one or two points) between different fuel brands, but the octane testing standards are the same.
Over the years working at the repair shop, I've often been asked about gasoline octane ratings. In the U.S., the numbers 87, 89, and 91 represent octane ratings - the higher the number, the better the fuel's resistance to knocking. Naturally aspirated engines typically run fine on 87 octane, but if you're driving a turbocharged or high-compression engine, using anything less than 91 might cause knocking that could damage your engine. Always check your owner's manual for the recommended octane rating before refueling - it's more reliable than gas station attendants' advice. Higher octane fuel won't make your car more fuel-efficient or cleaner; it's purely about meeting the engine's design requirements. Some gas stations sell ethanol-blended fuel, but the octane rating system still follows the same standards based on pure gasoline's anti-knock properties.
