The CO(A1&Pgr;) was produced with a nonthermal rotational distribution by impact of 30-eV electrons on CO2. The rotationally hot fourth-positive bands, CO(A1&Pgr;-X1&Sgr;+), were spectrally dispersed, and the reduced absorption of the (&ngr;',0) bands by thermal CO(300¿K) was measured (&ngr;'=0). The nonthermal bands are absorbed less strongly by CO(300¿K) than are thermal bands. The fractional transmission of the hot bands was measured over a wide range of CO absorber pressures (0-1000 millitorrs). The results lead to more accurate values for the slant column density and local number density of CO in the Mars upper atmosphere. The new values are 5.7¿1015 cm-2 and 1.5¿108 cm-3 at 150 km and 2.5¿1015 cm-2 and 6.8¿107 cm-3 at 170 km, respectively. The thermal and nonthermal sources of CO(A1&Pgr;) are shown to be of approximately equal strength at 170 km.