Carbon Monoxide is a colorless, odorless GAS that is highly toxic. It is produced when fuels such as gasoline, wood, coal, or natural GAS are burned incompletely. The three-letter solution for Carbon Monoxide is GAS. Inhaling this GAS can cause serious health problems, including death. It is important to be aware of the dangers of Carbon Monoxide and take steps to prevent it from accumulating in enclosed spaces.