A three-dimensional mathematical model for the pyrolysis of wet wood is developed with detailed consideration of moisture evaporation, anisotropic and variable properties, and pressure driven internal convection of gases. Multiple competing reactions are formulated; a single first-order Arrhenius reaction is however applied herein. Transient pyrolysis of a beech wood cube with different initial moisture contents is investigated under various furnace temperatures. Influences of anisotropic properties due to the grain structure on heat and mass transfers are discussed. This model serves as a precursor for Part 11: Simulation of piloted ignition of wood in a cone calorimeter of this two-part study. (c) 2007 Elsevier Ltd. All rights reserved.