A quantitative model for gas-solid reactions has been used in order to analyze the effect of percolation on the evolution of the overall particle properties (particle size, overall porosity and reactive surface area) during gasification/combustion reactions. Simulations of gasification of porous reactive solid spheres under different reaction regimes have been performed. Additionally, the influence of apparent reaction order and solid porous structure on the variation of overall particle properties has also been included in the simulation results. The initial porous structure of the solid has been introduced by the pore size distribution and initial porosity, thus offering a realistic description of the solid pore network. The results include the variation of the overall solid properties during gasification under different reaction regimes (from chemical control to external mass transfer control). The influence of pore size distribution and initial porosity on particle transformations are also analyzed. The model was validated by comparing the simulation results with experimental data found in the literature.