Grant,
 
Thanks for the interesting information you provided on biodiesel as a source of renewable energy. (I'm just now responding because even though I'm subscribed to Environet, I don't get the postings, and I forgot to check the archives.) Brian mentioned the notion of EROEI (energy recovered over energy input), and gave figures of 10-30 for oil, with all of the alternatives other than nuclear fission as 15 or below. I suppose that relates to the high cost of biodiesel, with the crossover occurring as the EROEI for diesel from petroleum drops with diminishing availability. In any case, if taxed biodiesel were to become available at $5 per gallon, that would seem to put a cap on how vulnerable the world might become to reduced availability of conventional diesel. What are the implications for other uses for petroleum?
 
Gordon Davy 
Baltimore, MD 
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410-993-7399