Most solids are inherently porous, and many techniques have been developed to characterize the porous structure of solids. Among them the simple gas adsorption technique gives the largest amount of information. From a standard nitrogen adsorption isotherm, one can obtain data on the total pore volume, the BET surface area and the pore size distribution of the solid. However, still more information can be extracted if one can apply the recent developments on the percolation and fractal analysis to the isotherm. In this article, the fractal and percolation analysis on the adsorption isotherm will be reviewed. The emphasis is on the practical application of these theories and the interpretations of the results related to the porous structure. A minimum previous knowledge of the percolation and fractal theories is assumed.
