Comparison between H₂ and H I (21 cm) column densities for the known molecular-absorption-line systems at high-redshift. T_s = 1000 K (100 K) is adopted for associated (intervening) systems shown as circles (squares). The color of the symbols represents the redshift, as indicated by the color bar on the right, and the size of the symbol traces the velocity extent of the absorption averaged over the H I and H₂ components.