We calculate the equipotential contours, drift trajectories, and predicted proton energy spectra in the inner magnetosphere using combinations of dipole or Tsyganenko magnetic field models and Volland-Stern or Weimer electric fields models. We compare the results with observations of proton energy spectra at L=4--5 over a range of local times from the Active Magnetospheric Particle Tracer Explorers/charge-energy-mass instrument. We find that the trajectories, and in particular the source location in the tail and the exit location on the dayside, depend significantly on both the electric and magnetic field models. However, the predicted energy spectra in the inner magnetosphere depended almost entirely on the choice of electric field. Using the Weimer electric field gives less loss along the trajectories, which is usually in better agreement with the observed energy spectra. ¿ 2000 American Geophysical Union