We present a measurement of the microlensing optical depth toward the Galactic bulge based on the analysis of 15 contiguous 1 deg ^ { 2 } fields centered on ( l = 2. \hskip { -2.0 pt } ^ { \circ } 5 ,b = -4. \hskip { -2.0 pt } ^ { \circ } 0 ) and containing N _ { * } = 1.42 \times 10 ^ { 6 } clump-giant stars ( belonging to the extended clump area ) monitored during almost three bulge seasons by EROS ( Expérience de Recherche d ’ Objets Sombres ) .
We find \tau _ { bulge } = 0.94 \pm 0.29 \times 10 ^ { -6 } averaged over all fields , based on 16 microlensing events with clump giants as sources .
This value is substantially below several other determinations by the MACHO and OGLE groups and is more in agreement with what is expected from axisymmetric and non-axisymmetric bulge models .