Avgas

Avgas is a high-octane fuel used for aircraft and, in the past, racing cars. Avgas includes a number of additives in order to decrease volatility so it won't evaporate away as quickly, which is important for high-altitude use. The particular mixtures in use today are the same as when they were first developed in the 1950s and 60s, and therefore the high-octane ratings are achived by the addition of large amounts of tetra-ethyl lead, a fairly toxic substance that was outlawed for car use in most countries in the 1980s.

Many general aviation aircraft engines were designed to run on 87 octane, the standard for automobiles today. Direct conversions to run on automotive fuel, known as mogas in the industry, are fairly common. However the alloys used in aviation engine construction are rather outdated, and engine wear in the valves is a serious problem on mogas conversions.

In Europe avgas prices are so high that the entire GA industry is being wiped out. There are a number of efforts to convert the industry to diesel instead, which is common, inexpensive and has a number of advantages for aviation use. It remains to be seen if there is enough of a market left for this to occur.