For short‐pulse energy extraction from a CO2laser amplifier it is desirable to use multiline/double‐band amplification. Multiline/double‐band oscillation including up to nine lines was obtained simultaneously from the 9.6‐ and 10.6‐&mgr;m bands by placing an etalon perpendicular to the optical axis of a CO2laser and adjusting its thickness in the oscillator cavity. Improvement in energy extraction was corroborated in the region of saturation amplification using a 1‐atm electron‐beam‐controlled amplifier.