Electron energy loss spectrometers (EELS) for surface studies require a high energy resolution (▵E ? 3 meV) monochromatic electron beam with the highest possible current. In order to improve the transmission of such a device, and so the achievable current, a 3D simulation of electron trajectories taking into account space charge effects was performed for typical three lenses cathode systems, electrostatic cylindrical deflector analyzer (CDA 127°) and acceleration lenses. The results of the analysis are presented and their effects on the overall design of the device are discussed.