Lignin thermolysis at temperatures from 300 to 600 degrees C and holding times from 10(1) to 10(4) s was simulated by a mathematical model. Modeling entailed a statistical interpretation of lignin structure and thermolysis, which was combined with experimental pyrolysis pathways and kinetics derived from model substrates that mimicked the chemical moieties within lignin. The model simulated the temporal evolution of lignin thermolysis products in each of four categories: namely, (i) gas, comprising methane and carbon monoxide; (ii) aqueous liquid, consisting of water and methanol; (iii) tar, containing single-ring aromatic liquids, the majority related to guaiacol, catechol, and phenol; and (iv) a carbonaceous residue, of multiple-ring aromatic products. Quantitative comparisons were effected between the simulated product yields and experimental product yields reported in the extensive literature on lignin thermolysis. Simulated gas yields and the variation of CO/CH4 within them were in good agreement with experiments. Simulated aqueous liquid yields compared poorly to experiments, being an order of magnitude smaller than reported. Simulated tar yields were of the same magnitude as reported in the literature; the model also predicted the appearance of all of some 30 phenolic compounds that have been detected in lignin tars. Simulated residue yields at long times accorded well with final "char" yields reported in the literature. Finally, simulated weight loss kinetics compared favorably to both the shapes and magnitudes of experimental observations reported as a function of time.