The role of cascading in auroral or photoelectron excited atomic oxygen emission is investigated by calculating distorted wave electron impact cross sections for some 24 excited levels in O I. Cascading contributes ~75% of the effective emission cross section for 1304 ¿ and 1356 ¿. About 98% of the cascade component to these ultraviolet lines is fed through the respective 8446-¿ and 7774-¿ transitions, with the consequence that the 4368-¿ and 3947-¿ emissions are very weak. The cascade component to 1304 ¿ is strongly enhanced in an optically thick medium due to radiation trapping of the lines from the 3s' 3D, nd3D, and ns3S (n?4) levels to the ground state. The 1304-¿ emission cross section appropriate in the optically thick atmosphere is predicted to be a factor of 2 larger than the emission cross section measured in an optically thin laboratory experiment. Consideration of this effect is necessary to understand the measured atmospheric 1304-¿/1356-¿ ratio in terms of laboratory cross sections. Several recent atmospheric measurements on electron excited atomic oxygen 1304-¿, 1356-¿, 4368-¿, 7774-¿, and 1152-¿ lines appear to be consistent with our calculated results, which imply that the Stone and Zipf (1974) 1304-¿ and 1356-¿ laboratory cross sections may be systematically too large by as much as a factor of 2.