Factors that contribute to the uncertainty in quantitative analyses of surfaces by x-ray photoemission spectroscopy and Auger electron spectroscopy are considered. Quantification is usually based on the convenient but quite arbitrary assumption that the sample is homogeneous within the outermost few nanometers. This assumption can lead to uncertainties of several hundred percent in the analysis and, as a consequence, a meaningful quantification based on measured peak intensities alone is not possible. In contrast, the contribution to the uncertainty from other factors is much smaller. It is further pointed out that, when many factors contribute roughly equally to the error, even considerable improvements in the uncertainty of a single factor, have only little influence on the total error. It is therefore clear that in the future effort must be concentrated on the development of practical techniques to enhance the knowledge on the in-depth composition since, without this, no improvement can be expected even if a substantial improved accuracy of other factors is obtained. One such technique that relies on analysis of both the peak intensity and the peak shape is discussed and this technique seems to reduce the uncertainty considerably, to a typical level of 10%-20%, depending on the solid and surface morphologies.