What is carbon monoxide? Carbon monoxide (CO) is a colorless, odorless, tasteless gas that is produced by the incomplete combustion of fuels such as wood, natural gas, gasoline, diesel, kerosene, coal and charcoal. It is caused by lack of oxygen or a disruption in the burning process. Household items such as a furnace, water heater, stove, space heaters, charcoal grill and gas dryer can be sources of carbon monoxide, especially if they are not in proper working condition or have been installed improperly. Vehicle exhaust fumes from attached garages, as well as poorly operating fireplaces may also be a source of carbon monoxide. CO is poisonous to the body and is fatal at high levels or with long exposure.