A comparison of dual fluidized bed gasification of biomass with and without selective transport of CO2 from the gasification to the combustion reactor is presented. The dual fluidized bed technology provides the necessary heat for steam gasification by circulating hot bed material that is heated in a separate fluidized bed reactor by combustion of residual biomass char. The hydrogen content in producer gas of gasifiers based on this concept is about 40 vol% (dry basis). Addition of carbonates to the bed material and adequate adjustment of operation temperatures in the reactors allow selective transport of CO2 (absorption enhanced reforming-AER concept). Thus, hydrogen contents of up to 75 vol% (dry basis) can be achieved. Experimental data from a 120 kW(Fuel) (input) pilot plant as well as thermodynamic data are used to determine the mass- and energy-balances. Carbon, hydrogen, oxygen, and energy balances for both concepts are presented and discussed. (C) 2009 Elsevier Ltd. All rights reserved.