Trajectories of charged particles in the trail region of the earth's magnetosphere are studied numerically using a model magnetic field. It is shown that both trapped and untrapped trajectories can be categorized into three groups using two dimensionless parameters. One of the parameters is the ratio of the x and z components of the model magnetic field. The other is the ratio of the plasma sheet thickness to the particle gyroradius in the midplane. Previous trajectory studies are incorporated into our classification scheme which resolves a number of apparent contradictory conclusions among them. The untrapped particles are analyzed in terms of the cross-tail displacement, the displacement time, the scattering of the final pitch angle, and the coefficient of reflection off the plasma sheet. The results are used to predict the upper limit on particle energization during one neutral sheet interaction.