The K shell intensity ratios K-beta/K-alpha for 59 elements in the atomic region 16 <= Z <= 92 have been measured at excitation energies of 5.9, 59.5 and 123.6 keV. K X-rays emitted by samples have been counted by a Si(Li) detector with resolution 160 eV at 5.9 keV. The measured values were compared with the theoretical values calculated using Scofield's tables based on the Hartree-Slater and Hartree-Fock theories and available experimental values. Reasonable agreement is typically obtained between present and theoretical values. (c) 2006 Elsevier Ltd. All rights reserved.