An experimental study of synthesis gas production from simultaneous steam reforming and partial oxidation of methane using an ac corona discharge was conducted. The benefits of the combination of the two reactions reduce the pure oxygen requirement in the system and increase the thermal efficiency by transferring heat between the exothermic and endothermic reactions. The results show that the addition of water vapor greatly enhanced the conversions of methane and oxygen and improved the energy efficiency in an oxygen-lean system. The energy consumed to convert a methane molecule decreased dramatically from 68 to 13 eV/m(c) with an increase in the percentage of water vapor from 0 to 50% at a CH4/O-2 ratio of 5. At the conditions studied, input power had more influence on the methane and oxygen conversions than applied frequency.