The peak small‐signal gain and output energy of an electrically initiated chemical laser are measured for both HF and DF operation. For identical conditions of electrical discharge and gas mixture [SF6&sngbnd;H2(D2)&sngbnd;He], the DF laser small‐signal gain coefficient is about a factor of 2 below that for HF, while in the oscillator configuration the output energies for the two cases are equal. The gain threshold is determined for parasitic oscillations, which can be avoided only under medium conditions corresponding to relatively low output energy. The maximum parasitic‐free energy with DF is about ten times that with HF.