To examine the potential for thermal deactivation during pulverized coal combustion a high-temperature wire-mesh reactor has been used to prepare chars at heating rates of 10(4) K s(-1) temperatures up to 1800 degrees C, and hold times of 0-5 s, from two Argonne Premium coals: Pittsburgh No. 8, a high-volatile bituminous coal, and Pocahontas No. 3, a low-volatile high rank coal. Residual char reactivities to oxygen were determined using a nonisothermal TGA method. A comprehensive examination of the effect of preparation conditions on char reactivity is reported. Chars from the higher rank coal were relatively less reactive than chars from the lower rank coal prepared at lower temperatures, in line with accepted trends. At the higher temperatures (up to 1800 degrees C), more typical of full-scale pulverized coal combustion, the trend was reversed. Due to the greater propensity of the lower rank coal for thermal deactivation, high-temperature chars from the higher rank coal were found to be relatively more reactive than chars from the lower rank coal. High-temperature chars were also found to have reactivities comparable to utility fly ash carbons. Volatile yield and elemental release measurements suggested that thermal deactivation is likely to be a result of structural changes within the char matrix, rather than loss of heteroatoms from the structure.