The adsorption of three synthetic organic compounds (SOCs) (i.e., phenanthrene, biphenyl, and 2-chlorobiphenyl), with similar physicochemical properties but different molecular conformations (i.e., planar and nonplanar), by an activated carbon and an activated carbon fiber was investigated. The physical characteristics of the carbons were obtained from low temperature nitrogen adsorption isotherms using BET, DR, and DFT models. Their surface chemistry was characterized by water vapor adsorption, pH of the point of zero charge, acid/base uptakes, and elemental analysis. The results indicated that adsorbent pore structure characteristics and adsorbate molecular conformation are important in the adsorption of SOCs by porous carbonaceous adsorbents. To predict the adsorption of SOCs by activated carbons, accurate characterization of pore shape and size distribution in primary micropores is important. The results indicated that adsorbate molecules can access and fill more efficiently the slit-shape pores than ellipsoidal pores, whereas the ellipsoidal pores create higher adsorption potential than slit-shape pores. Both molecular conformation and dimensions of adsorbate affect the adsorption. Planar molecules appear to access and pack in slit-shape pores more efficiently as compared to nonplanar molecules. Nonplanar molecular conformation weakens the interactions between adsorbate molecules and carbon surfaces. © 2008 Elsevier Ltd. All rights reserved.