A cw O/CS2CO chemical laser has been operated at a chemical efficiency of 37.5%. This result was achieved by the use of N2O as a diluent whoseV‐Vtransfer effects on the chemically formed CO are such as to strongly enhance emission in the low vibrational bands. The free‐running oscillator spectra start atv= 12 → 11 and continue tov= 2 → 1, with more than 50% of the output in the low bands 6 → 5 to 2 → 1. These results again emphasize the importance of vibrational energy transfer in chemical laser media.