The energy distribution of positive ions incident on a grounded surface in a low‐pressure argon planar rf glow discharge system has been measured as a function of excitation frequency from 70 kHz to 13.56 MHz for both capacitive and direct coupling of the rf power to the excitation electrode. The results are interpreted by taking into consideration both the transit time for the ion to traverse the sheath relative to the period of the rf excitation voltage, and the resistive or capacitive characteristics of the sheaths. The importance of system geometry and of the dc potential of the excitation electrode (as determined by external circuitry) on the maximum energy of ions incident on grounded surfaces is shown.