The growing use of bioenergy goes hand in hand with a heated public debate, in which conflicting claims are made regarding the amount of biomass that can be sustainably used for this purpose. This article assesses the current knowledge on biomass resource potentials and interrelated factors such as water availability, biodiversity, food demand, energy demand and agricultural commodity markets. A sensitivity analysis of the available information narrows the range of biomass potentials from 0–1500 EJ/yr to approximately 200–500 EJ/yr in 2050. In determining the latter range, water limitations, biodiversity protection and food demand are taken into consideration. Key factors are agricultural efficiency and crop choice. In principle, global biomass potentials could meet up to one third of the projected global energy demand in 2050.