Bivariate kernel density estimate of the fraction of CO-dark H₂ gas vs. the H₂ column density measured from CO (i.e., ignoring CO-dark H₂ gas) for all pointings. The shade scales with the density of points. The black curves serve as guides to compare the location of the probability peaks in different pointings. Plots are ordered according to the location of the main peak with respect to the black curves.