The study used a technique called 13 C-NMR to look at the structure of different parts of coal. They found that one type of coal component called inertinite has more aromatic compounds and less aliphatic hydrocarbons compared to another type called vitrinite. As coal matures, both inertinite and vitrinite become more aromatic, but inertinite does so more slowly. The process of aromatization is more pronounced in vitrinite than in inertinite. Inertinite also has lower oxygen content than vitrinite.