A detailed study is presented of the influence of several parameters on the energy-loss probability of fast electrons (∼100 keV) incident on small metallic spherical particles. We consider the collective modes of the sphere, including bulk-type modes which do not appear to have been considered previously in the literature. A Gaussian distribution is used to describe the electron in the plane transverse to the trajectory. We discuss the effects of the variation of several parameters—incident beam size, probe velocity, radius of the sphere, impact parameter, and the excited mode—and conclude that the absorption spectra depend critically on the geometry of the probe as the experimental data of Batson and Treacy suggest.