The characterization of the porosity of three samples of commercial activated carbons, from adsorption isotherms of N-2 (77 K), obtained by the volumetric method are presented. Special care was taken in the measurement of the isotherms in the range of low relative pressures (10(-6)) in order to characterize the microporosity of these carbons by different; approaches: Dubinin-Radushkevich (D-R), a plots, Jaroniec-Choma (J-Ch), and Pfeifer et al. Microporosity characterization was completed by measurement of the specific surface area (BET) of the adsorbents in which different amounts of benzene at 295 K had been preadsorbed. It was established that the three samples are basically microporous, with a strongly pronounced structural and energetic heterogeneity.