Output pulse observations are presented for a helium-diluted HF laser pumped by the H2+ F2chain reaction. Initiation of the reaction was accomplished with 180 transverse electrical discharges. Addition of a trace of O2to the gas mixture was found to enhance performance. Optimum performance was found with a 120-torr mixture with mole ratio F2:H2:O2:He = 1:0.7:0.08:15 initiated with a 22.5-kV 250-pF discharge; this gave a single-pulse output energy of 0.073 J. This corresponds to a ratio of laser output energy to electrical input energy of 115 percent.