A study is presented of a possible future measurement of the longitudinal structure function FL(x,Q ) with different proton beam energies at HERA. To appear in the proceedings of the workshop “Future Physics at HERA”, DESY, Hamburg, 1996. Future Measurement of the Longitudinal Proton Structure Function at HERA L.A.T. Bauerdick, A. Glazov, M. Klein a DESY, Notkestraße 85, D-22607 Hamburg, German...