Bremsstrahlung isochromat spectra have been recorded at ℏω0=9.7 eV for clean- and oxygen-covered Ni(100) and Ni(111) surfaces. Angle-integrated and normal incidence angle-resolved spectra are presented. In angle-integrated spectra, ordered c(2×2) and p(2×2) oxygen overlayers on Ni(100) and Ni(111), respectively, cause strong emission enhancement just above the Fermi level. This is attributed to adsorbate-induced antibonding empty electronic states. Energetic position and width of these states is different on the two crystal faces. Normal incidence spectra behave similarly upon oxygen adsorption but are more complicated due to extra emission from strong direct interband transitions.