Radial profiles of electron intensity and phase space density in the energy range of ~0.7 to 8 MeV, between L values of 3 and 9, show that particle injections followed by fast radial diffusion lead to the main part of the outer radiation belt near L=4 to 5 during active periods. In quiet times the belt is supplied by inward diffusion from an external source. Various combinations of these two basic configurations are also seen.¿ 1997 American Geophysical Union