Pitch/substrate interactions at the mixing stage (< 200 degrees C) were studied by means of a drop spreading wetting test. The substrates were obtained from a petroleum pitch by thermal treatment in the temperature range of 300-1900 degrees C. The results show that thermal treatment has a significant influence on the physical and chemical properties of the substrates, and consequently, on pitch/substrate wetting behaviour. Substrates with plastic properties (softening point below 350 degrees C) deform and/or agglomerate during the wetting experiment and thereby stop pitch penetrating. Moreover, the presence of aliphatic hydrogen in these substrates facilitates oxidative stabilization, which in turn facilitates pitch/substrate wetting behaviour. Substrates obtained above 400 degrees C are wetted by the pitch. However, the pre-graphitic order obtained on carbonization does not seem to have a significant effect on pitch wetting capability under the conditions used in this study. The oxidative stabilization of the substrates does not exert a significant influence on unfused substrates. However, in the case of plastic substrates, pitch wetting capacity is greatly affected by oxidation. (c) 2006 Elsevier Ltd. All rights reserved.