In this study, plasma reforming of n-dodecane for the co-generation of COx-free hydrogen and C-2 hydrocarbons at low temperature and ambient pressure has been investigated in a gliding arc discharge (GAD) reactor. The selective synthesis of H-2, C2H2 and C2H4 and the energy efficiency for n-dodecane conversion can be tuned by changing different processing parameters including the gas flow rate, n-dodecane concentration and input voltage. The highest selectivities of H-2 (76.7%), C2H2 (41.4%) and C2H4 (12.0%) were achieved with an n-dodecane conversion of 68.1%. The generation of mixed hydrogen, acetylene and ethylene offers the possibility for in-situ hydrogenation to enhance the selectivity of light olefins (e.g., ethylene) without prior gas separation. The plausible reaction mechanism and pathways in the plasma cracking of n-dodecane have been discussed through plasma emission spectroscopic diagnostics coupled with a comprehensive analysis of gas and liquid products. A strong correlation between the yield of C-2 hydrocarbons and the relative intensity of C-2 Swan bands was found, which suggests that C-2 Swan bands could be used as a valuable probe to understand the generation of C-2 hydrocarbons in the plasma reforming of hydrocarbon oils. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.