Energetic particle events observed upstream of the bow shock can have two possible sources, shock acceleration of solar wind particles or leakage from the magnetosphere. Three-dimensional global fluid simulations in conjunction with particle tracking in global fields are used to investigate the sources of the energetic particles. Acceleration of particles from the bow shock can account for many of the lower intensity events but the magnetosphere appears to be an important source during the more energetic particle events where 2 MeV particles are observed. ¿ American Geophysical Union 1996