X-ray spectra of K-shell hollow krypton atoms produced in single collisions with 52 -197 MeV/u Xe 54+ ions are measured in a heavy-ion storage ring equipped with an internal gas-jet target. Energy shifts of the 𝐾𝛼 1,2 𝑠 , 𝐾𝛼 1,2 ℎ,𝑠 , and 𝐾𝛽 1,3 𝑠 transitions are obtained. Thus, the average number of the spectator L-vacancies presented during the x-ray emission is deduced. From the relative intensities of the 𝐾𝛼 1,2
𝑠and 𝐾𝛼 1,2 ℎ,𝑠 transitions, the ratio of K-shell hollow krypton to singly K-shell ionized atoms is determined to be 14 -24%. In the considered collisions, the K-vacancies are mainly created by the direct ionization which cannot be calculated within the perturbation descriptions. The experimental results are compared with a relativistic coupled channel calculation performed within the independent particle approximation.