Previous investigations have found that the plasma catalytic conversion of methane is a low-temperature process for the activation of methane, the major component of natural gas. In this paper, the production of acetylene via plasma catalytic conversion of methane over NaY zeolite is discussed. Hydrogen is produced as a by-product during this plasma catalytic methane conversion. A methane/hydrogen feed with oxygen as an additive and helium as a diluent has been studied in this investigation. The CH4/H-2/O-2 system is found to be more selective for the production of C-2 hydrocarbons, compared to the CH4/O-2, CH4/H2O, and CH4/CO2 systems reported previously. A higher hydrogen concentration feed is more favorable for acetylene formation. The selectivity and yield of C-2 hydrocarbons are related to the hydrogen feed rate, gas temperature, concentration of oxygen additive, and flowrate. The highest yield of C-2 hydrocarbons (32%) is obtained at the lowest flowrate used (10 cm(3)/s; residence time similar to 2.3 s). A reaction mechanism is also presented to explain the experimental results,