To destruct tar from pyrolysis and/or gasification, an externally oscillated gliding arc plasma reformer (EOPR) was designed and verified its decomposition performance. The external oscillation device can give to expand the discharge area of the gliding arc plasma reformer. An experiment was conducted using surrogate benzene, which is generated during the pyrolysis and/or gasification, as the representative tar substance. To identify the characteristics of the influential parameters of tar decomposition, tests were performed on the oscillation frequency and amplitude, steam feed rate, and total gas feed rate. The optimal operating conditions of the EOPR were 267 Hz in oscillation frequency, 3 V-pp oscillation amplitude, 0.66 L/min in steam feed rate, 0.12% in benzene concentration, 16.7 L/min in total gas feed rate, and 0.17 kWh/m(3) in SEI (specific energy input). The benzene decomposition efficiency was 90.7%, and the energy yield was 22.95 g/kWh. Without oscillation, the decomposition efficiency was 82.6%, and the energy yield was 20.9 g/kWh, both of which were 8.9% lower than those with the external oscillation. Tar benzene was decomposed into light gases (H-2, CO, and CO2), hydrocarbons (CH4, C2H4. and C2H6) and carbon block. (c) 2012 Elsevier B.V. All rights reserved.