This paper describes experiments and theory relating to CO laser action in various CO mixtures with N
2and/or He. Short-pulse electron beam excitation of

s produced laser output between 1600 and 1900 cm
-1; the most intense line was at 1788.4 cm
-1and the shortest pulses of 4 μs duration were generated in the CO:He mixture. Although the calculated maximum efficiency was 7 percent, the maximum measured efficiency was 3 percent.