Abstract <p>The energy characteristics (losses of switched energy in the spark gap, which go to light emission, ionization, excitation, and heating of the working gas during the development of plasma processes; as well as the instantaneous released power, which serves as an energy source for the above processes) of hydrogen two-electrode spark gaps of the subnanosecond range have been studied in a wide pressure range (10–60 atm). The effect of runaway electrons on the energy characteristics of hydrogen spark gaps has been studied. For these purposes, the reflectometry method for measuring pulse voltages in the study of subnanosecond self-sustained discharges in gas is modified as follows. The plasma resistance of the discharge gas gap, which changes with time at the switching stage, is replaced by a constant resistor in those sections of the voltage waveform, where the characteristic ionization time exceeds the duration of the voltage pulse applied to the gap by more than an order of magnitude. This made it possible to reconstruct the voltage drop across the discharge gap measured at the breakdown stage, which cannot be correctly recorded in the subnanosecond range due to the presence of parasitic inductance of the measuring path. The voltage and current waveforms obtained in this way allowed us to calculate the dynamics of power and the total energy introduced into the gas-discharge plasma.</p>