rf impedance, dc self‐bias, and ion sheath (dark space) thicknesses are measured in an O2discharge for 7–53 Pa pressure and 50–800 W rf power (13.56 MHz). Special attention is paid to corrections for reactor stray impedances. It is concluded that the discharge can be described as a capacitance (the ion sheath) with both a parallel and a series resistance, the series element being the more important one. Good agreement is found between optical and electrical measurements of the ion sheath thickness. Evidence is presented that the dc potential difference between plasma and ground and rf electrode can be estimated with reasonable accuracy from the dc self‐bias and the optical dark space thicknesses. Positive ion acceleration in the ion sheath and electron‐neutral collisions in the bulk of the plasma glow account for only part of the total rf power transfer. It is suggested that significant dissipation takes place near the glow‐sheath boundary, although a quantitative description cannot be given yet.