Plain English Meaning

100LL is the blue-coloured petrol used by most small piston-engine aeroplanes. It has a high octane rating so the engine runs smoothly, and it still contains a small amount of lead -- less than older aviation fuels, but more than car petrol.

Full Definition

A grade of aviation gasoline (avgas) with an octane rating of 100 and a reduced lead content compared to earlier high-lead avgas formulations. It is dyed blue for visual identification and is the most widely available piston-aircraft fuel in the United States. It is approved for use in most reciprocating (piston) aircraft engines that require a 100-octane fuel.

Context Anchor

You will see 100LL at fuel pumps, on fuel trucks, in , and during fueling checks.