Using diluted methane/air mixtures in internal combustion engines has a potential of reducing emissions and increasing efficiency. However, the ignition systems used today show difficulties igniting lean mixtures. For this purpose a new high frequency (HF) ignition system using pulse generators and a resonance circuit to achieve a controlled number of sparks during a controlled period of time has been developed. A first prototype of this high frequency system has been tested in a flow-reactor and compared to a conventional ignition system.Results show that the high frequency system improves the flame development under lean conditions compared to the conventional system. Higher frequencies have higher capability of igniting lean mixtures than lower frequencies. Lower spark frequencies were found to travel faster across the electrodes than high frequencies and also compared to the conventional system. High pressure and high flow rates affected the lean limit of all ignition strategies, but especially high spark frequencies had difficulties igniting the charge under high pressures, due to the resonant frequency changing with pressure. The high frequency system was also limited in the amount of available voltage. However, this will be improved with further development of the ignition system.