Three coals were combusted in the Alberta Research Council laminar flow combustor in order to understand the changes in the physical structure that occur during pulverized coal combustion. A subbituminous (coal A), and both high-volatile (coal B) and low-volatile bituminous (coal C) coals were chosen to examine coals of different rank and reactivity. The subbituminous coal and the high-volatile bituminous coal were very reactive, with burnouts of 95% and 88% achieved under stable operating conditions. The low-volatile bituminous coal was relatively unreactive. It was not possible to achieve a stable flame with the burnout decreasing below 50% in less than 1 h. Direct comparison of the partially burnt samples from the three coals was difficult because of the different reactivities. The subbituminous and high-volatile bituminous coals burned so rapidly that it was not possible to collect samples below 70% burnout. Conversely, it was not possible to generate samples of low-volatile bituminous coal char at burnouts above 72%. The subbituminous coal showed a continuous decrease in particle size with burnout. The high-volatile bituminous coal showed a significant size decrease only before 70% burnout, whereas the low-volatile bituminous coal actually increased in size up to 60% burnout, followed by a slight decrease. Surface area analysis of the subbituminous coal indicated a large surface area contained in micropores. At high levels of burnout (above 90%), the surface area decreased. The same behavior was observed for the high-volatile bituminous coal. While the low-volatile bituminous coal also showed this large increase in surface area, the decrease occurred at about 50% burnout, much earlier than for the other coals. Results of mercury porosimetry tests on the partially burnt samples revealed a significant change in the pore volume for both the subbituminous and high-volatile bituminous coals, while no large changes were observed for the low-volatile bituminous sample. It was difficult to draw any conclusions from the porosimetry results due to the different particle size of the chars and wide variance in the measurements.