Clean-burning ethanol fuel may have a not-so-clean-burning secret.

Ethanol, made from corn and other renewable resources, is promoted as a fuel that burns cleaner than gasoline and helps reduce greenhouse gas carbon dioxide.

However, it takes a lot electricity to make ethanol, and power companies say the most cost-effective way to produce that electricity is from coal.

Environmentalists say that coal is the nation's biggest source of carbon dioxide.

They say more earth-friendly fuels like natural gas should be used to produce the needed electricity.