A decade ago plant-based fuels held tremendous promise in the U.S. The hope was that they would reduce reliance on foreign oil and cut greenhouse gases caused by burning fossil fuels. Ethanol made from corn took off, helped by a government mandate requiring billions of gallons of corn ethanol to be added to gasoline and diesel. But last month the Obama administration signaled it is rethinking the biofuel mandate. This has corn growers and developers of advanced biofuels up in arms. On the other side is the oil industry and environmental groups. For this month's Environmental Outlook: the battle over ethanol policy and the future of biofuels.