In order to fully understand the effect of formation pressure on resulting char properties, high-temperature and high-pressure pyrolysis experiments were conducted on three bituminous coals and a lignite. To simulate high temperature, high heating rate industrial processes, a flat-flame burner was designed and used within a high-pressure drop tube reactor. Chars were prepared at different pressures (1-15 atm) and analyzed. The mass release during pyrolysis was measured and compared to the modeling results of the Chemical Percolation Devolatilization Model (CPD). CPD model predictions based on elemental compositions of the parent coals agreed well with all measured results results. The physical properties of all char samples were analyzed, including swelling ratio, morphology, and surface area. Chars produced at high pressure were found to be in the early stage of foam structure evolution, and have a higher porosity but denser skeleton. The internal surface areas of char decrease with increasing char formation pressure, which contributes mostly to the low intrinsic reactivity of char formed at high-pressure.