The modifications in the development of fluidity of a single coking coal caused by Eucalyptus wood, its carbonization products (charcoal and tars) and biomass model compounds (xylan, cellulose and lignin) were assessed by Gieseler plastometry. Eucalyptus sawdust and its carbonization products obtained at 415 degrees C (tars and charcoal) inhibited the fluidity development of coking coals to different degrees. At a low addition rate, the following reducing effect on coal fluidity by biomass products and components was observed: xylan < water-soluble tar < charcoal < lignin < water-insoluble tar < cellulose < sawdust. As the amount of each biomass-derived carbonization product was increased in the blend, the overall effect resembled that of the biomass precursor (xylan, cellulose and lignin). In order to explain the different abilities of biomass-based additives to reduce the fluidity of coal, FTIR spectroscopy and GC-MS were used to identify the major components of the tars, while thermogravimetry was applied to follow the pyrolysis behavior of the biomass products and model compounds. (C) 2012 Elsevier Ltd. All rights reserved.