The researchers separated different parts of subbituminous coals and studied how they react to being turned into liquid. They found that liptinite is the easiest to turn into liquid, followed by vitrinite, and then inertinite. Inertinite needs higher temperatures to turn into liquid compared to vitrinite. Liptinite has more hydrogen, while vitrinite has more oxygen and inertinite has more carbon. They also looked at the densities and structures of these parts.