Determination of the variation of absolute and relative electron-excited x-ray production rates as a function of electron beam energy and sample atomic number is necessary for calculation of the "stopping power" atomic number correction and the relative amount of characteristic fluorescence and for development of “standardless” and Monte Carlo algorithms for quantitative x-ray analysis. Critical to the calculation of x-ray production rates is an accurate expression for the inner shell electron ionization cross section. A large number of expressions have been proposed for the relative x-ray production rates (used in the fluorescence correction)1 and for the ionization cross section used in the atomic number correction, and these yield quite different results. In order to evaluate which expressions gave the most accurate results when applied to quantitative x-ray emission measurements, we performed a series of high precision measurements of x-ray intensities as a function of electron beam accelerating potential for a series of pure element and simple oxide, phosphide, sulfide, and chloride standards for 65 elements ranging in Z from C to U