The present investigation was undertaken to determine the adsorption characteristics of nano-scaled porous carbons using a gravimetric adsorption technique through CCl4 and NH3 adsorption studies in the two different relative pressure ranges. Nanoscaled pore volumes (WO) determined from CCl4 adsorption isotherms were generally in good agreement with the BET surface area. However, the adsorption capacity of NH3 in the very low relative pressure range was independent of the surface area of the carbon samples. This can be attributed to the presence of a greater number of active adsorption sites related to higher density of surface oxygen and surface oxygen functional groups on the lower surface area carbons. The degree of surface area development and nano-scaled pore volume control the adsorption process in the high relative pressure range, and the surface chemistry affects the adsorption process in the very low relative pressure range. (c) 2004 Elsevier B.V. All rights reserved.