A molecular mechanics-molecular dynamics computer simulation method was used to model the swelling behavior of the pyridine-insoluble (PI) fraction obtained from Upper Freeport bituminous coal, an Argonne premium coal sample. Methanol molecules were successively added to a model compound for the PI fraction under periodic boundary conditions. After each addition, the energy of the system was minimized using molecular mechanics methods, and then molecular dynamics computations were performed. The swelling behavior was estimated from the incremental volume changes of the model compound and added methanol. The swelling ratio obtained from the simulation, 1.20, was in excellent agreement with the experimentally obtained value of 1.19.