Molecular hydrogen mass distribution of the HRS galaxies in bins of 0.4 in log. The molecular gas mass is determined assuming a constant X_CO factor (left panel) or the luminosity dependent X_CO factor given in Boselli et al. (2002) (right panel). The distribution is compared to the one derived by Oberschkow & Rawlings (2009) from the CO luminosity distribution of Keres et al. (2003) assuming a constant (red dotted line) or a luminosity dependent (blue dashed line) X_CO conversion factor. The vertical black dotted line indicates the completeness in M(H₂) of the HRS sample.