  We spectroscopically analyzed a sample of 85 Sloan Digital Sky Survey
compact, oxygen-dominated galaxies located at redshift $z\sim0.001-0.350$,
selected because of their large equivalent width of [O III]$\lambda$5007
(larger than 200\AA). These galaxies might be considered as extreme
emission-line galaxies due to their strong [O III]$\lambda$5007 emission line.
We detected high-ionization lines, even those related to the presence of
Wolf-Rayet stars, in almost all the galaxies studied. We obtained physical
properties (electron density and temperature) as well as chemical abundances by
using the direct method based on the electron temperature. In this analysis, we
obtained three different measurements of T(high): the usual one, T([O III]),
but also that of T([S III]) and T([Ar III]) for five and three of the galaxies,
respectively. Further, we established a new calibration for T([S III]). We
determined oxygen, nitrogen, sulfur, neon, argon, iron, and chlorine abundances
when possible, and we compared to the results of other late-type,
low-metallicity galaxies, such as blue compact dwarfs, Ims, and green peas.
From such a detailed study, we can conclude that the majority of the galaxies
in this sample have similar metallicities to the SMC (about
$12+\log(O/H)\approx8$dex), and that only 12% of the galaxies are extremely
metal-poor, with abundances lower than $7.7$dex. Also, a comparison with some
chemical evolution models as well as a brief discussion on the chemical
evolution with time is considered.
