Synthetic fuel was produced in Germany from the end of the 1920's onwards ! For turning it into
high-octane aviation fuel, lead tetraethyl was added, for getting it, the I.G. Farben got a license
from the US company Standard Oil (despite a veto by the then US government) in 1935. From the
beginning of the war, the refineries for synthetic fuel were the main and at the latest from 1942/
1943 the only source for aviation fuel. During WW II the US developed a new type of aviation fuel,
using trimethylpentane. That fuel had a higher octane-number, so allowed a higher compression
and power output. But that technology and the needed raw materials were hardly available in Germany
and until VE-Day no factory with high production was ready. So for German high-octane fuels other
additives had to be used, still limiting the octan-number and short in supply, too.
The history of the German fuel production is a very interesting theme on its own, not the least due
to the above mentioned "co-operation". Further reading is recommended here, I once read Joseph
Borkin "Die unheilige Allianz der I.G.Farben" (in English it's "The Crime and Punishment of I.G. Farben",
I think), though with hindsight this book was more a novel, than a serious historical report.
But there are information online, too, that allow for hours and hours of reading !
