  We present a new analysis of the main empirical calibrators of oxygen
abundance for ionised gas nebulae. With that aim we have compiled an extensive
sample of objects with emission line data including the near IR [SIII] lines
and the weak auroral lines which allow for the determination of the gas
electron temperature. For all the objects the oxygen abundances have been
derived in a homogeneus way, using the most recent sets of atomic coefficients
and taking into the account the effect of particle density on the temperature
of O$^+$. The residuals between directly and empirically-derived abundances as
a function of abundance have been studied. A grid of photo-ionisation models,
covering the range of physical properties of the gas, has been used to explain
the origin of the uncertainties affecting each abundance calibrator. The range
of validity for each abundance parameter has been identified and its average
uncertainty has been quantified.
