The energetic conversion of biomass into syngas or biogas is a more and more important topic. In the framework of these studies, improved understanding of glucose and fructose thermal decomposition and oxidation appears crucial. For this task, thermodynamic data are needed to make possible, for instance, the building of a detailed chemical kinetic model of glucose and fructose reactivity at high temperature. A semitheoretical protocol, presented elsewhere, is used for the estimation of the thermodynamic data of glucose and fructose in the gas phase. Five isomers of glucose and five isomers of fructose are considered and the lowest-energy conformers are found to be beta-D-glucopyranose for glucose and beta-D-fructopyranose for fructose. The data for all 10 isomers are provided in the CHEMK1N-NASA format. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.