The conglomerating characteristics of asphaltenes play an important role in the colloidal stability and the coking characteristics of residue during thermal reaction. These characteristics of asphaltenes derived from a Middle East atmospheric residue (MEAR) and its thermal reaction samples were studied. The characteristics focused here are the values of conglomerating parameters. A series of asphaltenes solutions are prepared in toluene for surface tensions measurement. The surface tension to logarithmic of concentration of asphaltenes exhibited break points in the range of 0.010-0.012 g g(-1). Furthermore, the molecular weight can be gained from the data of surface tension below the break point. Asphaltenes are in less conglomerated state than VPO MW measurement because the concentration is lower than that. Hence, the ratio of VPO MW to the molecular weight obtained by the surface data directly indicates the conglomerating parameter. It is further shown that asphaltenes tending to aggregate are prone to coke during thermal reaction. (c) 2005 Elsevier Ltd. All rights reserved.