Incipient coke formation was studied by heating a heavy hydrocarbon residue in isothermal batch reactor at atmospheric pressure of nitrogen at temperatures 320, 357, and 387 degrees C over times from 0 to 7 It. The kinetics of coke formation was followed by solvent extraction (insolubility in hexane (HI), toluene (TI)) and as development of HI and TI approximate to apparent first-order kinetics. Results appeared to follow the Wiehe's phase separation model for coke formation. The density of the pyrolysis residues was found to be independent of condition and it shows a linear relation to TI content. (C) 2007 Elsevier Ltd. All rights reserved.