Experimental measurements of absorption and emission by nonisothermal CO2 and H2O gases are reported. Analytical formulations and calculations of radiant heat transfer using a simple nongray gas model are presented. It is found that a gray gas model cannot predict even qualitatively the experimental results, while the band model method of calculation yields results in quantitative agreement for total emission and absorption in a band. Effects of line structure are shown to be of secondary importance compared to band envelope structure for line-width-to-spacing ratios above 10−2 in saturated bands. An analytical solution for coupled convection and radiation in a plane-parallel-wall duct is derived to illustrate the utility of the exponential band model for analysis of radiant transfer in nonisothermal, nongray gases.