The present paper demonstrates that the effective and hence the true critical energy E,. for direct initiation of gaseous detonations using electrical sparks corresponds to the total energy deposited into the gas up to the time trofthe peak averaged power, i.e., (E(t)/t)max, of the spark. The energy subsequent to this time is found to have no noticeable influence on the initiation processes. The method for demonstrating this experimentally is via the "crowbarred" discharge which was used to initiate cylindrically expanding detonation waves. Almost all previous investigations had implied that the direct initiation process can be characterized by a unique critical value of the source energy where the source energy was invariably taken as the total energy initially stored in the source or its equivalent. The present results indicate that the critical energy E,. is non unique but depends on its rate of deposition. It is found that E<. increases very rapidly with increasing time of energy deposition t,. However, a minimum limiting value of the critical energy is found to exist as tr-+ 0. The present results, in fact, suggest that the direct initiation process should be characterized by two parameters, namely, the peak power of the source and the energy release up to the peak power. The critical peak averaged power of the source, i.e., P,.=E,.(tr)/t, also exhibits a minimum value which corresponds to shock strengths of the order of the autoignition limit for the explosive mixture.