  We present a detailed and uniform study of oxygen abundance from two
different oxygen lines at 6158$\AA$ and 6300$\AA$ in a large sample of
solar-type stars. The results are used to check the behaviour of these spectral
lines as oxygen abundance indicators and to study the evolution of oxygen in
thick and thin disk populations of the Galaxy. Equivalent width measurements
were carried out for the [OI]~6158$\AA$ and OI~6300$\AA$ lines. LTE abundances
were obtained from these two lines in 610 and 535 stars, respectively. We were
able to measure oxygen abundance from both indicators in 447 stars, enabling
us, for the first time, to compare them in a uniform way. Careful error
analysis has been performed. We found that oxygen abundances derived from the
6158$\AA$ and 6300$\AA$ lines agree to within 0.1dex in 58\% of the stars in
our sample, and this result improves for higher signal-to-noise values. We
confirm an oxygen enhancement in stars of the thick disk, as has also been seen
for other $\alpha$-elements. The new oxygen abundances confirm previous
findings for a progressive linear rise in the oxygen-to-iron ratio with a slope
equal to 0.78 from solar metallicity to [Fe/H]$\sim$-1. However, the slope we
measured is steeper than the one found in previous studies based on the oxygen
triplet. Below [Fe/H]=$-$0.6 our stars show [O/Fe] ratios as high as $\sim$0.8,
which can be interpreted as evidence for oxygen overproduction in the Galactic
thick disk. These high oxygen abundances do not pose a problem to
chemodynamical models since there is a range of parameters that can accommodate
our results.
