The collisional removal of O 2 molecules in selected vibrational levels of the c 1 ⌺ u Ϫ state is studied using a two-laser double-resonance technique. The output of the first laser excites the O 2 to ϭ9 or 10 of the c 1 ⌺ u Ϫ state, and the ultraviolet output of the second laser monitors specific rovibrational levels via resonance-enhanced ionization. The temporal evolution of the c 1 ⌺ u Ϫ state vibrational level is observed by scanning the time delay between the two pulsed lasers. Collisional removal rate constants for c 1 ⌺ u Ϫ , ϭ9 colliding with O 2 , N 2 , and He are ͑5.2Ϯ0.6͒ϫ10 Ϫ12 , ͑3.2Ϯ0.4͒ϫ10 Ϫ12 , and ͑7.5Ϯ0.9͒ϫ10 Ϫ12 cm 3 s Ϫ1 , respectively. As the rate constants for O 2 and N 2 are similar in magnitude, N 2 collisions dominate the removal rate in the earth's atmosphere. For ϭ10 colliding with O 2 , we find a removal rate constant that is 2-5 times that for ϭ9 and that single quantum collision cascade is an important pathway for removal.