The efficiency of a gliding arc reactor designed with the aim to degrade aqueous phenol solutions is studied as a function of supply voltage, electrode gap distance, and gas-liquid flow properties. This efficiency, which steeply increases when increasing the supply voltage, can reach 96% when the minimum electrode distance is fixed at 3 mm. Experiments show that phenol degradation efficiency also depends on solution pH, Fe2+ addition, gas nature and gas flow rate. Furthermore, degradation pathways of phenol in aqueous solutions are proposed.