A Toast to '100LL'

Avgas is a high-octane fuel used for aircraft and racing cars. The term 'Avgas' is a portmanteau for aviation gasoline, as distinguished from mogas (motor gasoline), which is the everyday petroleum spirit used in cars. Avgas is typically used in aircraft that use reciprocating or wankel engines.

The most commonly used, 100LL, is dyed blue.  Spoken as "100 low lead", contains tetra-ethyl lead (TEL), a lead based anti-knock compound, but less than the "highly-leaded" 100/130 avgas it effectively replaced. Most piston aircraft engines require 100LL and a suitable replacement fuel has not yet been developed for these engines. While there are similar engines that burn non-leaded fuels, aircraft are often purchased with engines that use 100LL because many airports only have 100LL. 100LL contains a maximum of 2 grams of TEL per US gallon.