In article f3hWh.756$dM1.354@trndny07,
Justin Gombos wrote:

Out of curiosity, what's to stop the GA pilot (in terms of FAA law)
from making their own batch of biodiesel from waste oil to get rock
bottom prices, and sidestep the avgas tax entirely?

You must operate the aircraft (including the engine) iaw the limitations.
Those limitations will include minimum standards for the fuel. As long as
you could show your batch of diodiesel meets those standards, you
should be fine.

--
Bob Noel
(goodness, please trim replies!!!)