It won't burn in a liquid state. You could drop a lighted match into a bucket of heating oil and the oil would extinguish the flame, just like water. As a liquid, it can't combine with air to form an explosive mixture. Exposure to carbon monoxide is almost non-existent, compared to natural gas, propane, or wood heat. One of the cleanest combustion sources available.
Heating oil is a clear, rosy-red liquid that burns very clean.
It's a Good Value. Because of Oil Heat's high BTU content, it costs less per unit of heat produced. To equal the heat content of 1 gallon of heating oil, it takes 1.4 therms of natural gas, 1.52 gallons of propane, and 40.6 kwh of electricity.