The pyrolysis of gamma-valerolactone, a cyclic ester readily obtainable from cellulosic biomass and which has potential as a fuel, was investigated from 873 to 1113 K at 0.17 MPa in a tubular continuous flow reactor. Unimolecular decomposition of gamma-valerolactone forms 4-pentenoic acid and its selectivity increases upon addition of toluene, a radical scavenger. A kinetic model, consisting of 520 species and 3589 reactions, was developed. Kinetic and thermodynamic data relevant for gamma-valerolactone consumption, including hydrogen abstraction, hydrogen addition and fuel radical decomposition, were calculated at the CBS-QB3 level of theory. Experimental and calculated mole fraction profiles are in good agreement. Reaction path analysis shows that gamma-valerolactone is mainly consumed by isomerization to 4-pentenoic acid and hydrogen abstraction from the carbon atom a to the carbonyl group and the carbon atom alpha to the ring oxygen. C-C scission of 4-pentenoic acid forming allyl and carboxy methyl is an important source of radicals. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.