  We search for the maximum oxygen abundance in spiral galaxies. Because this
maximum value is expected to occur in the centers of the most luminous
galaxies, we have constructed the luminosity - central metallicity diagram for
spiral galaxies, based on a large compilation of existing data on oxygen
abundances of HII regions in spiral galaxies. We found that this diagram shows
a plateau at high luminosities (-22.3 < M_B < -20.3), with a constant maximum
value of the gas-phase oxygen abundance 12+log(O/H) ~ 8.87. This provides
strong evidence that the oxygen abundance in the centers of the most luminous
metal-rich galaxies reaches the maximum attainable value of oxygen abundance.
Since some fraction of the oxygen (about 0.08 dex) is expected to be locked
into dust grains, the maximum value of the true gas+dust oxygen abundance in
spiral galaxies is 12+log(O/H) ~ 8.95. This value is a factor of ~ 2 higher
than the recently estimated solar value. Based on the derived maximum oxygen
abundance in galaxies, we found the oxygen yield to be about 0.0035, depending
on the fraction of oxygen incorporated into dust grains.

Astrophysics