We report an energy-efficient biogas reforming process with high and stable methane conversions by O-2 presence. During this biogas reforming process, the effects of various O-2 concentrations in biogas on initial conversions and stability at various temperatures on a Ni/SiO2 catalyst were detailed investigated. In addition, theoretical energy consumption and conversions were calculated based on the Gibbs energy minimization method to compare with experimental results. Carbon formation and sintering during the reforming process were characterized by thermal gravity analysis, the Brunauer-Emmett-Teller method, X-ray diffraction, and high-resolution transmission electron microscopy to investigate the feasibility of applying this process to an inexpensive nickel catalyst. The results showed that 5% O-2 in biogas improved the CH4 conversion and stability of biogas reforming. The enhancement of stability was attributed to the inhibited sintering, our first finding, and the reduced carbon deposition at the same time, which sustained a stable conversion of CH4, and proved the applicability of base Ni catalyst to this process. Higher O-2 concentrations (>= 10%) in biogas resulted in severe decrease in CO2 conversion and greater H2O productivity. Our proposed biogas reforming process, with a high and stable conversion of CH4, reduced energy input, and the applicability to inexpensive base metal catalyst, offers a good choice for biogas reforming with low O-2 concentrations (<= 5%) to produce syngas with high energy efficiency. (C) 2016 Elsevier Ltd. All rights reserved.