Carbon monoxide is an odorless, colorless, and tasteless gas lighter than air. High levels of carbon monoxide can be fatal. Carbon monoxide is a toxic gas produced when fuels such as gasoline, oil, propane, kerosene, coal, wood, and natural gas do not have an adequate supply of oxygen to burn completely. When carbon monoxide is inhaled, it combines with the body's blood and prevents it from absorbing oxygen. Symptoms of carbon monoxide poisoning include severe headaches, nausea, vomiting, and sleepiness. There is usually no fever associated with carbon monoxide poisoning.