Each biofuel has advantages and disadvantages.

Ethanol
Since the early 1990s, ethanol has been blended into gasoline to reduce harmful carbon monoxide emissions. Blending ethanol into gasoline also reduces toxic pollutants found in gasoline but causes more "evaporative emissions" to escape. In order to reduce evaporative emissions, the gasoline requires extra processing before it can be blended with ethanol. When burned, ethanol does release carbon dioxide, a greenhouse gas. But growing plants for ethanol may reduce greenhouse gases, since plants use carbon dioxide and produce oxygen as they grow.

Biodiesel
Biodiesel is much less polluting than petroleum diesel, and when blended into traditional diesel fuel, can help reduce emissions. It results in much lower emissions of almost every pollutant: carbon dioxide, sulfur oxide, particulates, carbon monoxide, air toxics, and unburned hydrocarbons. Although biodiesel does produce nitrogen oxide emissions that are about 10 percent higher than what is produced by burning petroleum-based diesel.