  The oxygen dopants are essential in tuning electronic properties of
Bi$_2$Sr$_2$Ca$_{n-1}$Cu$_n$O$_{2n+4+\delta}$ superconductors. Here we apply
the technique of scanning tunneling microscopy and spectroscopy to study the
influence of oxygen dopants in an optimally doped
Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+\delta}$ and an overdoped
Bi$_{2-y}$Pb$_y$Sr$_2$CuO$_{6+\delta}$. In both samples, we find that
interstitial oxygen atoms on the SrO layers dominate over the other two forms
of oxygen dopants, oxygen vacancies on the SrO layers and interstitial oxygen
atoms on the BiO layers. The hole doping is estimated from the oxygen
concentration, as compared to the result extracted from the measured Fermi
surface. The precise spatial location is employed to obtain a negative
correlation between the oxygen dopants and the inhomogeneous pseudogap.
