The analysis of percolative fragmentation for noncatalytic gas-solid reactions, with special emphasis on gasification and combustion of carbonaceous materials, is presented. The description of pore surface area and pore surface enlargement during reaction is based on the random pore model developed by Bhatia and Perlmutter (1980, A.I.Ch.E.J. 26, 379-386; 1981, A.I.Ch.E.J. 27, 247-254). Different reaction regimes between intraparticle diffusion and chemical kinetics control are considered. The inclusion of percolative fragmentation in the Bathia-Perlmutter random pore model allows a more realistic description of changes during gasification of porous solids to be made. The results include the variation of local properties (porosity, surface area and gas concentration) within the particle at different reaction stages as well as the modification of the overall particle properties (particle conversion, percolated mass fraction and reaction rate) with reaction progress.