Reliability of chemical abundance determinations in H II regions

The reliability of the standard procedures for deriving helium, oxygen, nitrogen, neon, and sulfur abundances in gaseous nebulae and of a proposed procedure for deriving argon abundances is investigated through the calculation of model H II regions with normal abundances and single central stars. The errors encountered at each step are examined; the combined procedures give errors < or approx. =5% for helium and < or approx. =50% for the other elements in most cases. The errors are only slightly larger if the ionization is produced by an aggregate of stars with a range of spectral types. Problems can be encountered if several H II regions are observed simultaneously (as in extragalactic objects) but probably will not be important for situations which occur in nature. The procedures work very well for low-abundance high-ionization H II regions, as are found in other galaxies