The experimental study of capacitive radio‐frequency (rf) discharges was performed in mercury vapor at low pressures (10−4–10−2Torr) and at rf applied voltage below 200 V. It was found that at pressures less than 10−2Torr, plasma electrons gain rf energy basically through a noncollisional mechanism at the oscillating potential barrier formed in electrode sheaths. The rf power dissipated in this process turned out to be much larger than that received by electrons through their collisions with neutral atoms in the plasma bulk. Experimental results are in good agreement with the theoretical model of low‐pressure rf discharges developed earlier by one of the authors.