In high-resolution electron energy-loss spectroscopy (HREELS) with the specular-reflection geometry, a probed dispersion region determined kinematically depends upon the incident angle @alpha@ and the incident energy E@sub 0@. With change in @alpha@ and E@sub 0@, we make a kinematic analysis of the probed dispersion region with special attention to its width. Simultaneously, we evaluate the effect of the image force and the analyzer aperture on the probed region. Our analysis shows that, with a grazing angle @alpha@ fixed and with E@sub 0@ varied in a broad range, we can scan a sharply narrowed probed region on the wavenumber-energy (Q-@omega@) plane to make a close observation of the dispersion relation of surface-excitation modes. Even at grazing incidence, the image force has no substantial influence on the probed region, though it operates to reduce the energy-loss intensity remarkably at low E@sub 0@. When the parameter h@omega@/2E@sub 0@ becomes appreciable compared with the aperture angle, presence of the aperture causes a certain decrease in the width of the probed Q region. In the HREELS with the off-specular geometry, the incident energy E@sub 0@ is restricted to a lower range to insure sufficient intensity, and the probed dispersion region depends upon @alpha@ and an off-specular angle @theta@. With change in @alpha@ and @theta@, we make the same analysis of the probed dispersion region with close attention to its width as in the specular-reflection geometry. The results of this analysis for the off-specular geometry will also be reported at the conference.