Which three fossil fuels produce the least carbon dioxide?

If a free source of hydrogen exists then no CO2 is produced. Since hydrogen does not exist in high concentrations as a free form on the earth it must be made either through electrolysis of water or from processing natural gas in a refinery. The former is possible with any means of electricity and the amount of CO2 generated is dependent on the means of generation (coal, natural gas, wind, solar, hydroelectric, nuclear etc.)

The fossil fuel that releases the least amount of carbon dioxide is natural gas, which is mostly methane (CH4). This is due to the methane having the lowest carbon to hydrogen ratio of another fossil fuel source.