Infrared OH lines at 1.5 - 1.7 \mu m in the H band were obtained with the NIRSPEC high-resolution spectrograph at the 10m Keck Telescope for a sample of seven metal-poor stars .
Detailed analyses have been carried out , based on optical high-resolution data obtained with the FEROS spectrograph at ESO .
Stellar parameters were derived by adopting infrared flux method effective temperatures , trigonometric and/or evolutionary gravities and metallicities from Fe ii lines .
We obtain that the sample stars with metallicities [ Fe/H ] < - 2.2 show a mean oxygen abundance [ O/Fe ] \approx 0.54 , for a solar oxygen abundance of \epsilon ( O ) = \approx 8.87 , or [ O/Fe ] \approx 0.64 if \epsilon ( O ) = 8.77 is assumed .