The U.S. Energy Information Administration (EIA) explains that octane ratings measure a fuel’s stability and its resistance to engine knocking, or uncontrolled combustion, with ratings calculated as an average of motor and research testing methods. In the U.S., gasoline is classified into regular (87), midgrade (89-90), and premium (91-94) grades, with higher octane required for the increased pressure in many modern performance engines. Read the full story at EIA.
Gasoline explained – octane in depth – U.S. Energy … – EIA