The aim of this research work was to evaluate the possibility of upgrading the simulated biogas (70 % CH 4 and 30 % CO 2) for hydrogen-rich syngas production using a multi-stage AC gliding arc system. The results showed that increasing stage number of plasma reactors, applied voltage and electrode gap distance enhanced both CH 4 and CO 2 conversions, in contrast with the increases in feed flow rate and input frequency. The gaseous products were mainly H 2 and CO, with small amounts of C 2H 2, C 2H 4 and C 2H 6. The optimum conditions for hydrogen-rich syngas production using the four-stage AC gliding arc system were a feed flow rate of 150 cm 3/min, an input frequency of 300 Hz, an applied voltage of 17 kV and an electrode gap distance of 6 mm. At the minimum power consumption (3.3 × 10 -18 W s/molecule of biogas converted and 2.8 × 10 -18 W s/molecule of syngas produced), CH 4 and CO 2 conversions were 21.5 and 5.7 %, respectively, H 2 and CO selectivities were 57.1 and 14.9 %, respectively, and H 2/CO (hydrogen-rich syngas) was 6.9. The combination of the plasma reforming and partial oxidation provided remarkable improvements to the overall process performance, especially in terms of reducing both the power consumption and the carbon formation on the electrode surface but the produced syngas had a much lower H 2/CO ratio, depending on the oxygen/methane feed molar ratio. The best feed molar ratio of O 2-to-CH 4 ratio was found to be 0.3/1, providing the CH 4 conversion of 81.4 %, CO 2 conversion of 49.3 %, O 2 conversion of 92.4 %, H 2 selectivity of 49.5 %, CO selectivity of 49.96 %, and H 2/CO of 1.6. © Springer Science+Business Media, LLC 2011.