High resolution photoabsorption cross section data for the CO 4PG (1,0) band have been obtained under several different temperature conditions. It was found that the absorption strength of the d (3)Delta(1)-X (1)Sigma(+) (5,0) band underlying the 4PG (1,0) band varies with temperature. The ratio of the absorption band strength of the d-X (5,0) band to that of the 4PG (1,0) band has been determined for temperatures at 150 K, 295 K, and 370 K. Adopting the integrated oscillator strength of the 4PG (1,0) from the recent literature we have determined band absorption cross sections for the two bands as a function of temperature. The ratios of the band absorption strengths of the A-X (1,0) and d-X (5,0) bands at different temperatures are compared with those calculated from the mixing coefficients determined by analysis of level shifts in high resolution spectra and lifetime measurements.