  The Large Area Telescope (LAT) onboard the Fermi satellite is exploring the
gamma-ray sky in the energy range above 20MeV. We have developed a method to
reconstruct the energy spectra of the gamma rays detected by the Fermi LAT
instrument based on a Bayesian unfolding approach. The method has been
successfully applied to simulated data sets to reconstruct the energy spectra
of both steady and pulsating point sources. The basic ideas and the procedures
implemented to evaluate the energy spectra of gamma ray sources will be
illustrated, and the results of the application of the method to a typical test
case will be shown.
