Abstract Experimental K-shell ionization cross sections from the 1978 compilation by Gardner and Gray, and from some more recent publications, are presented graphically, for projectiles from 1H up to 19F. The cross sections were normalized by dividing the experimental results by values obtained with the PWBA theory, corrected for binding, polarization, Coulomb, and relativistic effects, according to Brandt and Lapicki. The normalized cross sections are plotted versus projectile energy or versus the scaled velocity variable ξ. In spite of some obvious discrepancies between different experiments, it is found that almost all the cross sections agree with the corrected PWBA theory within 60%. The majority of those measured with H, He, or Li projectiles are between 30% below and 10% above that theory. Many of the plots versus ξ show small systematic deviations from the theory, within those 60% limits: a minimum at ξ = 0.6, a maximum at ξ = 0.3, and a steep decrease below ξ = 0.2. The last feature might be due to a deficiency of the Coulomb correction.