Definition
A grade of leaded aviation gasoline with a minimum aviation lean rating of 100 and a minimum aviation rich rating of 130, used in higher-performance piston aircraft engines that require a high-octane fuel to resist detonation. AVGAS 100 is dyed green to distinguish it from other fuel grades.
Plain English
A type of high-octane piston-engine aircraft fuel that contains lead and is colored green so pilots and fuelers can tell it apart from other fuels at a glance.
Context Anchor
Seen in fuel-grade discussions, aircraft manuals, fuel placards, and fueling decisions for piston-engine aircraft.
Derivation
AVGAS is a contraction of 'aviation gasoline.' The number 100 refers to the fuel's octane-style performance rating — the higher the number, the better the fuel resists premature ignition (detonation) under pressure. Knowing this helps because the grade number directly tells you how much engine stress the fuel can handle before detonating.
Why Pilots Care
Selecting the correct grade prevents engine damage from detonation and keeps the aircraft airworthy.
Intuition Check
Do not read 100 as “100 percent” or “full-strength gas.” Here, 100 is a grade number showing how well the fuel resists harmful knocking in the engine.
Example Sentence 1
The POH specifies AVGAS 100 or 100LL as approved fuels for this engine.
Example Sentence 2
Before departure the pilot confirmed the tanks contained only AVGAS 100 as required by the POH.