In this paper we estimate the availability of shrub biomass along two different geographical transects in the Iberian Peninsula, i) North transect: NE-NW and ii) an Atlantic-Mediterranean transect: NW-S. To determine the available shrub area, the legal, technical, economic and environmental restrictions pertinent to the study areas were identified and their relative thresholds were established. Additionally, the amount of available shrub biomass (tonnes dry matter per hectare) along both geographical transects was calculated using equations specifically created for Spanish shrub formations. The NE-NW transect gave shrub biomass accumulations ranging from 11 to 16 t ha(-1), while the NW-S transect displayed much lower values, from 3 to 16 t ha(-1). Furthermore, the stored energy potential (gigajoules per hectare) for each shrub formation was calculated at each location. This paper provides realistic information, by shrub formation, on shrub biomass availability in the Mediterranean basin, highlighting the suitability of scrublands as potential sources of biomass, as well as the strengths and weaknesses of harvesting such biomass using machinery specifically designed for shrubs. (C) 2017 Elsevier Ltd. All rights reserved.