We describe procedures to propagate the uncertainty in adsorption data and as-values to generate uncertainty in apparent primary, secondary, and total micropore volumes for Porous activated carbons exhibiting Type I and IV character. The as-data are interpolated from selected non-porous reference material (NPRM) adsorption isotherm data with some adsorbents exhibiting surface chemistry quite different from and some similar to that of the Porous adsorbents (PA). We show that a statistically constant apparent total micropore volume can be determined independent of the NPRM Surface chemistry. In contrast, NPRM surface chemistry appears to influence our ability to identify unequivocally the filling and condensation ranges of micropore filling, leading to statistically different apparent primary and secondary micropore volumes. (C) 2008 Elsevier Inc. All rights reserved.