  A study of the precision of the semiempirical methods used in the
determination of the chemical abundances in gas-rich galaxies is carried out.
In order to do this the oxygen abundances of a total of 438 galaxies were
determined using the electronic temperature, the $R_{23}$ and the P methods.
The new calibration of the P method gives the smaller dispersion for the low
and high metallicity regions, while the best numbers in the turnaround region
are given by the $R_{23}$ method. We also found that the dispersion correlates
with the metallicity. Finally, it can be said that all the semiempirical
methods studied here are quite insensitive to metallicity with a value of
$8.0\pm0.2$ dex for more than 50% of the total sample.
  \keywords{ISM: abundances; (ISM): H {\sc ii} regions}
