Thermal depolymerization and decomposition of woody biomass structural components, such as cellulose, hemicelluloses and lignin, form liquids and gas products as well as a solid residue of charcoal. The direct thermo-chemical conversion technologies that have been developed are classified into two groups: high pressure liquefaction and fast pyrolysis. Bio-oils derived from biomass have been increasingly attracting attention as alternative sources of fuels and chemicals. The bio-oils were composed of a range of cyclopentanone, methoxyphenol, acetic acid, methanol, acetone, furfural, phenol, formic acid, levoglucosan, guaiocol and their alkylated phenol derivatives. The structural components of the biomass samples mainly affect pyrolytic degradation products.