This study compares the major biomass components (i.e., cellulose, hemicellulose and lignin) with respect to their differing tar formation characteristics during the gasification process. To better understand the tar formation mechanism, the tar content and composition were analysed via gas chromatography coupled with mass spectrometry (GC-MS). The tar yields of the three components all decreased with increasing temperature or excess air ratio (ER). However, lignin has a higher tar yield and produces more stable components in tar due to its molecular structure. At higher temperatures, the tar composition shifts toward higher-molecular-weight substances, such as polycyclic aromatic hydrocarbons (PAHs). For lignin, PAHs are derived primarily from phenols and its derivatives. For cellulose and hemicellulose, PAHs are derived primarily from benzene, toluene, ethylbenzene and xylene isomers (BTEX) and miscellaneous hydrocarbons. During the gasification process of real biomass materials, it is crucial to remove the tar compounds derived from lignin for tar control. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.