Discrepancies in the results obtained during the adsorption of nitrogen, argon, and water on two mesoporous samples are compared and contrasted. A silica-based mesoporous oxide and the same sample coated with a film of polystyrene were chosen with respect to their different surface chemistries. The nitrogen BET surface is overestimated on the pure silica sample and underestimated for the polymer-coated sample. These differences can be related to the specific interaction (strong or weak) of nitrogen with these surfaces. Water has difficulty in wetting either surface. Moreover, in the case of the polymer-coated material, water is unable to fill the mesopores via capillary condensation. (C) 2004 Elsevier Inc. All rights reserved.