A novel plasma shade with large reactive space generated by rotating spark channels was used for the first time for oxidative reforming of simulated biogas (CH4:CO2:O-2 = 3:2:2) to produce high-concentration syngas (CO + H-2) with low energy cost. This unique plasma exhibited rapid- and slow-zones where the conversion of O-2, CH4 and CO2 and dry-basis concentration of syngas (C-CO+H2(dry)) changed at two significantly different paces with specific energy input (SEI). With increasing SEI, the conversion and C-CO+H2(dry) first increased rapidly at SEI < 84 kJ/mol, while the conversion and C-CO+H2(dry) increased at a much slower pace at SEI > 84 kJ/mol. Moreover, V-shape profile of syngas energy cost (ECCO+H2dry) versus SEI was observed. Thereby, the optimal SEI was found at which the lowest ECCO+H2 (1.0 eV/molecule) and a very high C-CO+H2(dry) (73%) were simultaneously achieved. The good stability of the plasma reaction at the optimal SEI was verified over an 8-hour test.