An attempt was made to convert some agricultural and forest residues, including oak wood waste, corn hulls, and corn stover, into activated carbons. Microporous activated carbons were produced by physical activation with CO2 as the activation agent; specifically, the effects of activation temperature and duration were explored. The resultant activated carbons were characterized by measuring their porosities and pore size distributions. The activated carbons produced had the BET surface areas ranging from 400 to 1000m(2)/g, and ratios of micropore volume to total pore volume ranging from 0.38 to 0.66. The pore size distributions (PSDs) were narrow and peaked approximately at a pore diameter of 0.5 nm. Both the surface area and the nature of porosity were significantly affected by the conditions of activation, the extent of which depended on the nature of the precursors. In general, the higher the activation temperature, the greater are the surface areas and micropore volumes of the resultant activated carbons. Nevertheless, various precursors were affected differently by the duration of activation. For oak, the longer the duration of activation, the greater the adsorption capacity of resultant activated carbons, and vice versa for corn hulls and corn stover. (C) 2004 Elsevier B.V. All rights reserved.