Using grazing-angle, ion-induced electron emission spectroscopy at clean and oxygen-covered metal surfaces (Al, Cu, Fe, Ni(110) and Pd(110)), the authors have studied the angle-resolved energy distribution (ARED) of emitted electrons which directly reveals details of the initial electron excitation mechanisms. The authors find that secondary electron cascades are strongly suppressed and that the ion-induced electron excitation occurs predominantly at the topmost surface layer. The major excitation mechanisms for electron emission are single electron excitation via decay of surface and bulk plasmons (for 150 keV H⁺ ions), electron-hole pair excitation and Auger electron excitation.