The physical processes involved in x-ray preionization of high-pressure avalanche-discharge gas lasers are reviewed to determine optimum preionizer parameters. Preionization of lasers such as XeCl, CO2 etc., requires an x-ray dose of ~1mR. More strongly attaching rare-gas-fluoride lasers (e.g. KrF) require stronger preionization (> 10 mR per pulse). X-ray generation by electron-beam sources is discussed and candidate cathode types are reviewed. Typical preionizer pulsed-power2 parameters are 100 kV pulses of 100 - 200 ns duration, electron-beam current density of lA cm-2 and repetition rate of ~100 pps.