When determining the capacity of National Forests to develop sustainable bio-energy systems, accurate estimates of forest biomass are needed. What appears to be a straight forward assessment of biomass availability is complicated by the existence of highly variable data sets. Country level data is mostly produced by scaling data from a few sites to the country level. Using Indonesia as a case study, reported data varied by more than 20%. Using the reliable data, three levels of biomass potential, namely the lower and upper bounds (5,083 million Mg and 10,726 million Mg, respectively) and moderate estimates (5,410 million Mg) at the country level are constructed.