100LL

100LL is a grade of aviation gasoline (AVGAS) used to power most piston‑engine aircraft. The “100” denotes its octane rating, while the “LL” stands for low lead, indicating a reduced tetraethyl lead content compared with older high‑lead grades such as 100/130. The fuel is dyed blue to distinguish it from automotive fuels and other aviation fuels.

100LL is designed for spark‑ignited aviation engines and is not intended for turbine (jet) engines or most diesel aviation engines. The lead additive provides anti‑knock properties that enable high‑compression operation in many light aircraft engines. The fuel is produced to meet industry specifications for AVGAS and is widely available at general aviation airports in many regions, particularly in North America and Europe.

Concerns about lead emissions have driven efforts to find unleaded alternatives. Some engines and airframes can operate on unleaded fuels with appropriate certification, and new unleaded high‑octane options have been developed to replace or supplement 100LL in numerous installations. One notable example is G100UL, an unleaded 100‑octane AVGAS introduced to expand options for operators. However, not all existing engines are certified for unleaded substitutes, and 100LL remains the most common AVGAS in use today.

In summary, 100LL is the conventional high‑octane, low‑lead aviation gasoline associated with piston‑engine aircraft, balancing performance with historical lead content while facing ongoing industry shifts toward unleaded alternatives.