An autothermal fluidized bed reactor was used to carry out research on the influence of pressure on gasification process of different types of biomasses. The gasified feedstocks were bark, lignin and softwood pellet as a reference material. The gasification was done with a mixture of O2/CO2/H2O. The impact of the application of CO2 on yield of H2 in syngas was determined. Resulting high content of CO makes use of the syngas in chemi­cal synthesis applications very difficult without pretreatment . On the other hand, the CO2 proved to improve Car­bon Conversion Efficiency of the gasification and to be an option for its chemical sequestra­tion (negative carbon footprint). Moreover, a slight variation of conventional indices used to evaluate efficiencies of gasification systems (Carbon Conversion Efficiency and Steam/Carbon ratio) was proposed to take into account the impact of the additional source of carbon. Increasing system pressure led to syngas changes in line with predictions of the Le Chatelier's principle. The changes were seen primarily by higher yields of CH4 and lower overall production of syngas. For higher hydrocarbons (CxHy) the trend was unclear. For each pressure level and a standard 850°C gasification temperature, a set of stable gasification parameters were achieved with the exception of lignin at 2 barg.