Gas mass functions predicted by our SAMs. The colour code is explained in Table 1. For comparison, we add the extremal gas mass function deduced from the dark-matter mass function and the universal baryonic fraction ⟨f_b⟩ (grey dashed-line). In the case of m₄, we plot the total (star-forming + no-star-forming) and the star-forming gas mass function. We compare our results with the molecular gas mass function computed by Berta et al. (2013; lower limits, circles) and with the local HI mass function computed by Zwaan et al. (2005; triangles). The black solid line shows the HI mass function predicted by Lagos et al. (2011), using Bower et al. (2006) SAM. The horizontal arrows show the link between the density and the number of haloes in our simulation volume.