In this study, thermogravimetric (TG) analyses, along with thermal and catalytic fast pyrolysis experiments of cellulose, hemicellulose, lignin and their mixtures were carried out in order to investigate their pyrolysis products and whether the prediction of the pyrolysis behavior of a certain lignocellulosic biomass feedstock is possible, when its content in these three constituents is known. We were able to accurately predict the final solid residue of mixed component samples in the TG analyses but the differential thermogravimetric (DTG) curves indicated limited heat transfer when more than one component was present in the pyrolyzed sample. The limited heat transfer did not have a significant effect on the TG curves but it affected the product distribution in the fast pyrolysis experiments, which resulted in inaccurate calculation of the product yields, when using a simple additive law. In addition, the pyrolysis products of each biomass constituent were characterized in order to study their contribution to the yield and composition of the products from whole biomass pyrolysis. An investigation into the pyrolysis reaction pathways of each component was also carried out, using the bio-oil characterization data from this study and data found in the literature.