cw output of 1.1 W was attained from a compact (14‐cm discharge length, 2‐mm bore diameter tube) sealed‐off CO waveguide laser operating in the HE11 mode. The BeO laser tube, cooled to 210 °K, was operated at the 1‐W level for more than 4 h without output degradation and with a 5.7% efficiency. A mixture of CO:He:Xe:N2 in the ratio of 1:8:1:1, at a total pressure of 80 Torr, was found to be optimum, confirming the scaling or similarity rule of the product of optimum pressure and tube diameter for CO at this temperature. The output spectrum consisted of about 10 lines, between 5.20 and 5.65 μ. Laser operation without N2 (1:8:1:0) was also observed. Black particles found in the tube were x‐ray identified as Ni plus NiO, indicating sputtering from the Ni cathode.