What the market will bear.

http://green.autoblog.com/2010/04/20/report-biodiesel-tax-credit-bill-expected-on-obamas-desk-by-en/

a 1$ per gallon tax credit for Bio Diesel could easily be paid for by adding a $1 per gallon tax on oil, or super sized slurpees, or any number of liquids that we really need people in this country to start consuming less of. Really. put a tax on McDonalds 32oz, 230cal sweet tea to pay for something that might actually be beneficial for us as a species. Really! Dare to Dream!