In order to investigate the influence of pressures up to 9 bar absolute on the productivity of trickle-bed reactors for biological methanation of hydrogen and carbon dioxide, experiments were carried out in a continuously operated experimental plant with three identical reactors. The pressure increase promises a longer residence time and improved mass transfer of H-2 due to higher gas partial pressures. The study covers effects of different pressures on important parameters like gas hourly space velocity, methane formation rate, conversion rates and product gas quality. The methane content of 64.13 +/- 3.81 vol-% at 1.5 bar could be increased up to 86.51 +/- 0.49 vol-% by raising the pressure to 9 bar. Methane formation rates of up to 4.28 +/- 0.26 m(3) m(-3) d(-1) were achieved. Thus, pressure increase could significantly improve reactor performance.