Which fuel, natural gas or heating oil, is more environmentally friendly?

It is generally conceded that natural gas is the cleaner burning fuel. While the clean rating is based on a number of factors, natural gas is the better overall performer. Emission effects chart How does natural gas compare to the new "clean" heating oil? When compared to the new cleaner-burning, blended furnace oils, natural gas is still the more environmentally friendly fuel, especially in terms of Total Particulate Matter, Carbon Monoxide and Nitrogen Oxides.