  We propose a methodology to perform a self-consistent analysis of the
physical properties of the emitting gas of HII galaxies adequate to the data
that can be obtained with the XXI century technology. This methodology requires
the production and calibration of empirical relations between the different
line temperatures that should superseed currently used ones based on very
simple, and poorly tested, photo-ionization model sequences. Then, these
observations are analysed applying a methodology designed to obtain accurate
elemental abundances of oxygen, sulphur, nitrogen, neon, argon and iron in the
ionsied gas. Four electron temperatures and one electron density are derived
from the observed forbidden line ratios using the five-level atom
approximation. For our best objects errors of 1% in T([OIII]), 3% in T([OII])
and 5% in T([SIII]) are achieved with a resulting accuracy between 5 and 9% in
total oxygen abundances, O/H. These accuracies are expected to improve as
better calibrations based on more precise measurements, both on electron
temperatures and densities, are produced.
