This study is focused on both experimental and theoretical analysis of fast pyrolysis of guaiacol, a major pyrolysate and a model monomeric compound of lignin. Fast pyrolysis experiments were performed in an analytical pyrolyzer coupled with gas chromatograph/mass spectrometer in the temperature range of 450-650 degrees C. Thermodynamics and kinetics of 19 elementary reactions of 17 species were investigated using quantum chemical density functional theory calculations. Reaction pathways for the formation of four major phenols, viz. phenol, catechol, o-hydroxybenzaldehyde and o-cresol, were proposed. The homolytic cleavage of O-CH3 bond, with low bond dissociation energy of 57.7 kcal/mol, is shown to be the primary reaction for the generation of free radicals. The generation of o-hydroxyphenyl radical is found to be vital for the formation of phenol and cresol, while o-hydroxybenzyloxy radical is the key intermediate for the formation of o-hydroxybenzaldehyde. Multiple pathways for the formation of catechol were evaluated. A kinetic model was developed using the elementary reactions and their Arrhenius rate parameters. The concentration of the major products at different temperatures obtained from the model reasonably matched the trends in product yields from the experiments. (C) 2019 Elsevier Ltd. All rights reserved.