Last week US ethanol producer Bioenergy said it plans an initial public offering (IPO) of its stock of as much as $300 million.

It would become the latest company scrambling to tap into the green stream flowing out of the ethanol business–and in the US, the ethanol business right now means corn.

Rising demand for ethanol in the context of the price of oil has triggered a financial stampede. The share price of agri-giant Archer Daniels Midland (ADM)–which produces about one-quarter of the ethanol in the US–is up 68% so far this year, and ethanol providers VeraSun, Pacific Ethanol and Aventine Renewable Energy have all had lucrative, successful IPOs this year.

An enthusiastic Patricia Woertz, CEO of ADM, told investors and analysts during the recent second-quarter earnings announcement that demand for ethanol could quickly rise to an amount equivalent to 10% of the fuel pool nationwide.

But there is equally rapidly growing concern among the some in both the scientific and investment communities that the corn-fueled ethanol boom is not sustainable.