Electra is a repetitively pulsed, double-sided, electron-beam pumped krypton fluoride laser. Electra has recently operated as an oscillator with an output pulse of 510 J, with 100 ns pulse duration for single shots. At a 1 Hz repetition rate for a ten-shot burst, the laser output averaged 500 J per shot. The dependence of the laser energy on the partial pressures of Kr, Ar, and F2 were examined. Over a 10 to 30 psi total pressure range, the laser output energy decreases with decreasing argon concentration. Specifically, the laser output drops slightly as the argon concentration reduces from 60% to 40%, and then drops more noticeably as it is reduced to 0%. For the 60% Ar case, the optimal fluorine concentration is 0.25%, with a significant falloff in the laser energy from 0.25% to 0.1% and a gradual falloff from 0.25% to 0.7% fluorine. The present burst results indicate that the KrF kinetics is not very sensitive to the gas temperature at a total pressure of 20 psi. © 2004 American Institute of Physics.