Data are presented on the energy extraction from a transversely excited atmospheric CO2 laser amplifier by a 1.1‐ns pulse consisting of an adjustable number of lines which are generated by a multiline oscillator of a new design. An increase in energy extraction of 95% with respect to single‐line extraction was achieved with a pulse consisting of up to six lines in the 10.6‐μm branch. Energy extraction at a fixed number of lines was not very sensitive to their spectral distribution. We observed a maximum increase of about 8% when the lines were spread over the 00°1–10°0 vibrational band. This indicates a slight preference for small Δj values in the rotational relaxation processes.