The increase of the share of renewable energy sources in Portugal can be met from different sources where biomass plays a main role. This paper presents an estimation of the quantity of biomass residuals from the forest, wood industry, agriculture and agro-industry. For the forest residues, three methodologies were used based on: i) Forest clear area, ii) Forest area and trees rotation and iii) Wood production. The values obtained are based on data from the wood forest in 1995 and in data from wood production, agriculture and agro-industry from 1997 to 1999. The total amount of pine and eucalyptus residues amounts to 650 - 1045 thousand tons/year in dry basis and is lower than other estimative from other authors. The differences obtained between the methods are analyzed as a function of the assumptions made and the relative merits. Additionally, the residues produced from holm oak and cork oak are estimated as 128 thousand dry ton/year. The wood industry and cork industry contributes with a residues production around 1584 thousand dry ton/year, while the total amounts of residues produced in agriculture and agro-industry are estimated as 2001 and 872 thousand dry tons/year, respectively. Considering technical and economical limitations and alternative utilization of biomass residues, the total amount available for combustion is estimated around 2628 thousand dry ton/year and it; seasonal distribution is identified.
