Twenty-three solar carbon monoxide lines are analyzed with respect to their equivalent widths at the center of the disk and their increase toward the limb. Excitation temperatures of 4550 K at cos 0 = 1.0 and 4590 K at cos 0 = 0.2 are determined. The method of weighting functions is used to test the accuracy of the uppermost strata of models published by Aller and Pierce, by de Jager, and by Minnaert by means of their ability to predict the observed equivalent widths and center-to-limb behavior. The composite model proposed by Minnaert appears to be the most satisfactory of the three considered. The logarithmic abundance of carbon determined from this model is 6.72, when the logarithmic abundance for hydrogen is 10.00. The influence of a lateral temperature structure in this model is explored.