We report ion energy distributions (IEDs), relative ion intensities, and absolute total ion current densities at the grounded electrode of an inductively coupled Gaseous Electronics Conference (GEC) radio-frequency (rf) reference cell for discharges generated in pure C2F6, c-C4F8, and in mixtures of each gas with Ar. These discharges contain several ions of significant intensity, with the dominant ion seldom that expected from direct ionization of the feed gas. Neither the C2F6 nor the C-C4F8 fraction in the Ar mixtures significantly influences the reactive ion composition. IEDs vary from single peaked to bimodal, the latter indicating rf modulation of the ions' energy as they traverse the plasma sheath. Elevated gas pressures and higher fractions of either C2F6 or c-C4F8 all result in comparatively broader and more bimodal IEDs. IEDs in pure c-C4F8 discharges, compared to C2F6 discharges, generally exhibit more pronounced broadening and bimodality. [S0734-2101(00)01106-4].