The properties of polycapillary x-ray fibers at medium energies for applications such as crystal diffraction and mammography have been extensively measured and reported. However, many medical and industrial applications for x-rays, such as chest radiography, x-ray orthovoltage therapy, and nondestructive testing, require higher x-ray energies, up to or exceeding 100 keV. In order to investigate the feasibility of using Kumakhov capillary x-ray optics on these applications, measurements have been performed on the behavior of capillary optics at higher energies. Transmission efficiency of straight polycapillary fibers of different types have been measured as a function of source location and x-ray energy from 10 to 80 keV. The measurements are compared to geometrical optics simulations, which have also been extended to these energies. Despite the lower critical angle for total external reflection at high energies, capillary x-ray optics appear promising for many applications.