A volumetric apparatus for adsorption measurement of hydrogen in carbonaceous materials aimed at hydrogen adsorption storage was constructed. The performance of the apparatus was assessed by helium and hydrogen adsorption in one kind of vapor-grown graphitic nanofiber (GNF). The bulk gas amounts determined by the equations of state of the Modified-Benedic-Webb-Rubin (MBWR), the ideal gas and the Soave-Redlich-Kwong (SRK) under the conditions of present study are compared. Two different methods of processing experimental data to determine the residual volume are studied. Experimental results and theoretic analysis showed that the volumetric apparatus and the data processing method described in this paper could accurately determine the Gibbs excess adsorption amount of hydrogen in carbonaceous materials. Although the vapor-grown GNF used in the present study did not show a significant storage capacity of hydrogen, the obtained results would provide favorable reference data for the development of the carbonaceous material for hydrogen adsorption storage. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.