An alternating-current (AC) gliding arc reactor has been developed offering a new route for the co-generation of syngas and value-added carbon nanomaterials by plasma dry reforming of methane. Different carbon nanostructures including spherical carbon nanoparticles, multi-wall carbon nanotubes and amorphous carbon have been obtained as by-products of syngas generation in the plasma system. Optical emission spectra of the discharge demonstrate the formation of different reactive species (Al, CO, CH, C-2, H-alpha, H-beta and O) in the plasma dry reforming reaction. The effect of different operating parameters (feed flow rate, input power and CH4/CO2 molar ratio) on the performance of the plasma process has been evaluated in terms of the conversion of feed gas, product selectivity and energy conversion efficiency. It is interesting to note that gliding arc plasma can be used to generate much cleaner gas products of which syngas is the main one. The results also show that the energy efficiency of dry reforming using gliding arc plasma is an order of magnitude higher than that for processing using dielectric barrier or corona discharges. Both of these can be attributed to the higher electron density in the order of 10(23) m(-3) generated in the gliding arc plasma. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.