The biomass inventories in selected geographical areas for both countries, Hungary and Greece are determined in this paper. Particular emphasis is given to low cost opportunity fuels. This type of fuels does not require biomass cultivation processes (fertilizer and irrigation) and consequently energy exploitation shows increased environmental benefits. Those fuels are frequently used to supplement fossil energy sources, such as coal and oil. They may be even used as the main fuel for specific boilers or kilns. This study refers to the European legislation which determines the framework for rational and environmentally friendly practices for wood waste management. It also refers to the wood waste classification systems and the currently applied methods of wood waste disposal and reuse. The available biomass potential is reflected for the selected areas of Hungary and Greece, on an annual basis in order to minimise problems of periodicity and to guarantee steady supply to the potential consumers.