  We report a measurement of the cosmic ray energy spectrum obtained using the
inclined events detected with the Pierre Auger Observatory. Showers with zenith
angles between 60 and 80 degrees recorded in the period between 1 January 2004
and 28 February 2007 are analysed. Showers are first reconstructed in arrival
direction and then fitted to density maps of the muon numbers obtained from 10
EeV simulated proton showers for different arrival directions, in order to
obtain the core position and an overall normalisation factor N19 which is used
as an energy estimator. The parameter N19 is shown to be correlated with the
shower energy measured with the fluorescence technique for a sub-sample of good
quality hybrid showers. This correlation, measured with hybrid events, is then
used to determine the energy of all the showers.
