The Food and Agricultural Organization (FAO) reported that 3,339,000 ha of forest exist in the region of the Middle East, of which 1,658,000 ha are located to Iran. It was also reported that each hectare has the potential to produce 80 m3 of biomass [2]. Thus, the output of Iranian forests has the potential of 133 million cubic meters or 331 million tons of biomass, annually. Efficient use of this resource could generate 218 TWh electricity [1]. As mentioned earlier, livestock waste is one of the main resources available for biogas production in Iran. It is obvious that varied climate conditions are an important consideration for keeping domestic livestock and Iran has suitable climate conditions, therefore good potential for significant amounts of biomass production. Therefore planning for production of biogas from livestock manure is an attractive option that needs to be highlighted in planning and policy development agendas for renewable energies.
The contribution of different biomass resources for biogas production in the world is shown in Table 1 which demonstrated that the agricultural solid waste and livestock manure most important ones with higher values. Preliminary investigations revealed that the Iran׳s biomass potential is equal to 15 million tons or 140 million barrels of crude oil equivalent, and that is equal to 13% of Iran׳s total crude oil production in the year 2010[1]. According to variety and diversity of biomass resources, different methods for resource assessment (calculations of available and accessible resources) are applicable. These methods can be applied for analysis and assessment of biogas production from Livestock manure in Iran.