The operation of a CW CO2laser is reported in which a flow-conditioning technique is used to produce a uniform discharge at atmospheric pressure with a specific input in excess of 500 J/g. In this technique the premixed gas is introduced radially at sonic velocity through a narrow gap adjacent to the upstream electrode. A theoretical and experimental examination of the conditions for the appearance in the discharge of fine filaments, which can be regarded as incipient arcs, gave an insight into the method of operation of the technique. A laser is described that uses a cascade of six 0.2-m-long 19-mm-ID discharge tubes in which the gas flow, discharge, and optical axes are along the length of the tubes. The output power of 530 W at about 5-percent efficiency was limited by the difficulty of power extraction from the low-gain, high-saturation-flux medium.