  This is the fifth paper in a series studying the stellar components, star
formation histories, star formation rates and metallicities of a blue compact
galaxy (BCG) sample. Based on our high-quality ground-based spectroscopic
observations, we have determined the electron temperatures, electron densities,
nitrogen abundances and oxygen abundances for 72 star-forming BCGs in our
sample, using different oxygen abundance indicators. The oxygen abundance
covers the range 7.15 < 12 + log (O/H)< 9.0, and nitrogen is found to be mostly
a product of secondary nucleosynthesis for 12 + log (O/H)>8.2 and apparently a
product of primary nucleosynthesis for 12 + log (O/H)< 8.2. To assess the
possible systematic differences among different oxygen abundance indicators, we
have compared oxygen abundances of BCGs obtained with the Te method, R23
method, P method, N2 method and O3N2 method. The oxygen abundances derived from
the Te method are systematically lower by 0.1-0.25 dex than those derived from
the strong line empirical abundance indicators, consistent with previous
studies based on region samples. We confirm the existence of the
metallicity-luminosity relation in BCGs over a large range of abundances and
luminosities. Our sample of galaxies shows that the slope of the
metallicity-luminosity relation for the luminous galaxies (~-0.05) is slightly
shallower than that for the dwarf galaxies (~-0.17). An offset was found in the
metallicity-luminosity relation of the local galaxies and that of the
intermediate redshift galaxies. It shows that the metallicity-luminosity
relation for the emission line galaxies at high redshift is displaced to lower
abundances, higher luminosities, or both.
