aviation gasoline (avgas) - high-quality gasoline manufactured under stringent controls to meet the rigorous performance and safety requirements of piston-type aircraft engines. Volatility of aviation gasoline is closely controlled since, in most aircraft engines, excessive volatility can lead to vapor lock. Aviation gasolines generally have lower vapor pressure and a narrower distillation range than automotive gasolines (see distillation test). Aviation gasolines are formulated to resist chemical degradation and to prevent fuel system corrosion. There are two basic grades of aviation gasolines (based on their antiknock value): 80 (80 lean/87 rich) and 100 (100 lean/130 rich). Aviation gasoline has different properties than turbo fuel, which fuels gas-turbine-powered aircraft. See lean and rich octane number.