The airport terminal in Sioux Falls, S.D., could be anywhere, until you reach the baggage claim area. Between the carousels is a green and white Indy-style race car, covered with decals that indicate it runs on ethanol. Approach the rent-a-car booths, and you will see a sign taped to the countertop reminding customers not to pump E85, the ultraethanol blend sold locally, into the rental cars because they are not designed for it and it will ruin their engines.

This is ethanol country, the center of the national push to turn carbohydrates into hydrocarbons.