The search for replacements for oil and natural gas is heating up, as the price of oil rises. No alternative is getting more attention than biofuels - which in the US means ethanol from corn or biodiesel from soybeans. The movement has terrific political momentum because it promises not only to increase the price of corn, but also to enrich those who have invested in distillation facilities. There are those like David Pimentel who claim that growing crops and processing biofuels requires more energy than is produced when they are burned, but his conclusions are disputed by the US Department of Agriculture among others. Even if bioethanol requires only 90% as much energy to produce as you get by burning it, it does not represent much of a greenhouse gain. More than thermodynamics is at issue. New Scientist has a nice, brief (four-page) article that describes some of the other concerns about biofuels - it explains that the potential of this energy source is limited (replacing ten percent of the gasoline/diesel used in the US would require 30% of the agricultural land in the country). By 2007, it is expected that bioethanol will be consuming one-fifth of the corn crop. Many question the wisdom and ethics of converting so much food to energy for transportation, and some environmentalists worry about the demands for water, pesticides, fertilizer, and marginal land that this supposedly "green" movement will gobble.