Arrange the following fossil fuels in increasing order of their carbon intensities (gC/MJ).

In increasing order of carbon intensity the sequence runs natural gas, then petroleum, then coal.

Statement 1, natural gas, has the lowest carbon per unit energy since it is rich in hydrogen and burns cleaner.

Statement 3, petroleum, sits in the middle with more carbon per unit energy than gas.

Statement 2, coal, has the highest carbon intensity as it is almost pure carbon with little hydrogen.

So the correct rising sequence places gas first, petroleum second and coal last.

This is why switching from coal to natural gas lowers carbon dioxide emissions for the same energy output.