Hydrogen-rich gas can be efficiently produced in compact plasma reformers by the conversion of a variety of hydrocarbon fuels, including natural gas and gasoline. This article describes experimental and modeling progress in plasma reforming of methane using a sliding discharge reactor (SDR). Experiments have been carried out in a compact device operating at low consumed power (1-2 kW). Previous studies of methane steam reforming using a SDR at atmospheric pressure show promising results (H-2 concentration higher than 55%). In order to study the effect of oxygen on the methane conversion and thus hydrogen production, a small amount of oxygen in the range of 7-20% was added to the CH4-H2O mixture. An unexpected result was that under our experimental conditions in the SDR oxygen did not have any influence on the methane conversion. Almost the totality of added oxygen is recovered intact. Moreover, part of the H2 produced was transformed into water by reaction with O-2. A model describing the chemical processes based on classical thermodynamics is also proposed. The results indicate that the reactor design has to be improved in order to increase conversion and hydrogen production.