The production of hydrogen and electricity from biomass is accomplished by reformation of bio-oil in fast pyrolysis processes. Pyrolysis oil concentrates most of the energy of biomass and is used for the production of electricity and heat in small-to-medium size stationery applications. This is achieved by using Molten Carbonate Fuel Cells (MCFC), which are hydrogen-utilizing fuel cells. Although the conversion of biomass into pyrolysis oil has been developed to a mature stage, the new products can be potentially harmful and with a variable energetic content. For this reason they have to be assessed before large-scale use. In this direction an analytical method of characterization of biomass and pyrolysis products has been developed. Three biomasses have been chosen as representative of different kind of feedstock for the fast pyrolysis: herbaceous energy crops (Switchgrass), woods (Beech) and residues (Pine sawdust). The feedstocks resulted in quite different morphology and chemical composition. Switchgrass had the higher content of organic extractives and ash. The content of calcium in Beech was relatively high while pine sawdust had the highest content of cellulose to which corresponded to a relatively low content of xylose. Beech wood had the highest calorific value. Moreover, the respective three-pyrolysis oils produced from chips of beech wood, pine sawdust and switchgrass obtained by fast pyrolysis have been investigated. The thermal behaviour, the elemental compositions and the water solubility have been studied both between the oils and in comparison with the starting biomasses. It has also been concluded that viscosity is the most sensitive parameters affecting aging. The three oils showed different behaviours on aging, with Switchgrass showing the least favourable. The analytical method for biomass and bio fuels characterization may comprise a valuable scientific and technological input to potential producers. Developed methods could help provide an answer to obtaining future energy sources.