The nature of the mass-transfer processes of volatile components released inside pulverized coal particles during pyrolysis is examined by means of a mathematical model. The particles are assumed to be spherical and nonswelling and to have no internal temperature gradients during heating. The thermal cracking of tars is incorporated. Devolatilization kinetics measured for two American lignites are used to give generation rates and the model output is compared to experimental results for these coals. The transfer processes modeled include pressure-driven Poiseuille (bulk) now and Fickian diffusion, as Knudsen diffusion does not apply. The internal overpressures generated are not great so that external pressure strongly influences the transport mode. Both bulk flow and diffusion are found to be active and are of the same order of magnitude at 10 atm. Above 1 atm external pressure, the ratio of mass transfer by bulk flow to diffusion increases. Thermal cracking is significant only above 1 atm and 750 degrees C.