We have studied the spatial distribution of arcing as a function of electrode spacing and preionization pattern in CO2laser discharge mixtures, using circular electrodes which allowed a gap of up to 10 cm and a discharge volume of ∼3 liters. We utilized both cathode‐field enhancement with uniform preionization and apertured preionization with uniform field to define the discharge boundaries. In both cases, we found a threshold value of cathode‐field enhancement below which arcing was uniform and confined to the discharge region and above which arcing became highly nonuniform, with arcs localized to the high‐field region.