We propose a new method to parameterize the transfer equation, when calculating outgoing thermal radiation, that allows one to minimize the errors introduced when taking into account the molecular absorption. We have analyzed the errors in data on the intensity and halfwidths of the spectral lines of six gases, namely of H2O, CO2, O3, N2O, CH4, and CO, compiled in the HITRAN-96 database. It is shown in this paper that the errors in the integral intensities of the absorption bands of the gases under study are within 3–10% while typical errors in the halfwidths of individual strong lines are about 10%. The majority of these estimates are the summed errors in the intensities of individual lines, thus being the upper estimates. In a number of spectral intervals, we have revealed systematic deviations in the integral intensities of the absorption bands. The computer modeling conducted has shown that the main contribution into the error in the intensity of outgoing radiation, detected with a HIRS radiometer, is due to systematic components of the errors in the integral intensity of the bands and line halfwidths.