Methane is converted to acetylene, ethylene, and ethane over carbon at atmospheric pressures using pulsed high-power radiofrequency or microwave radiation. By judicious use of experimental variables, selectivity of acetylene in hydrocarbon products can be >90%. The concentration of hydrogen has been shown to be important. To obtain a clearer understanding of the role of carbon in this system, experiments have been conducted using amorphous C-13. A mechanism is postulated to explain the contribution of carbon and hydrogen to the formation of higher hydrocarbons.