Log N(O I) as a function of log N_H I for the VMP DLAs of Cooke et al. (2011, triangles). The color of the triangles refers to their metallicity measured as [Fe/H] and reported in the side band. The solid black lines are approximately marking metallicities of [Fe/H] ≃  − 2, −3 and −4 (from top to bottom). The dotted black line indicates the column density threshold defining DLAs. The red lower limits on log N_H I are the O I absorbers in our sample, red circles indicate PDLA systems. Dark-red crosses mark estimated log N_H I for the latter systems, obtained from the fit of the red damping wing of the absorption.