Knowledge of the thermodynamic equilibrium and kinetic rate constants of competing reactions of xylooligomers during dilute acid pretreatment are extremely useful for optimizing the biomass conversion process.  Ab initio molecular dynamics and metadynamics simulations were used to investigate the energetics of several competing pathways encountered during dilute acid pretreatment. The processes studied include xylooligomer hydrolysis, the condensation reactions of xylose monosaccharide to disaccharides, and xylose degradation reactions.  The multi-dimensional free energy surfaces (FES) obtained allows accurate determination of both the reaction free energies and barriers of these reaction processes.  The thermodynamic equilibrium and the kinetic reaction rate constants were subsequently determined and compared with available experimental data.  The effects of solvent water on the free energies and barriers of the hydrolysis, degradation and reversion reactions were investigated.  The stabilities of disaccharides were also examined with consideration for their hydrogen bonding structures.