The energies predicted by four different source hypotheses for ions observed upstream of the earth's bow shock are compared with observations with observatins of upstream field-aligned beams and ''gyrating ion'' events. A kinematic formalism in a frame of reference in which the motional electric field vanishes is used. Specular reflection of a fraction of the incident solar wind is found to be the most credible explanation of gyrating ion events observed upstream of shocks ranging from quasi-parallel to nearly perpendicular. The recent hypothesis the field-aligned beams are the result of leakage from the magnetosheath of ions which were originally specularly reflected at quasi-perpendicular portions of the shock provides good agreement with observed energies of many field-aligned beams. Of the several source hypotheses examined, only magnetic moment conserving reflection of solar wind ions is capable of accounting of two very energetic beam events. Although the magnetic moment of an ion should not be conserved during a single encouter with the shock, it is possible that multiple encounters of ions which are originally specularly reflected at the shock can produce an upstream distribution of particles which appear to have conserved their magnetic moment.