Gas fraction distributions as a function of the redshift of model galaxies with SSFR > t_H(z)^-1 and M_∗ > 10¹⁰  M_⊙. The filled contours correspond to equally spaced values of the density (per Mpc³) of galaxies on a logarithmic scale: from 10^-3 for the lightest filled region to 10^-2.1 for the darkest. The plotted value of log f_gas is the median value for sources in four redshift bins: (0 < z < 0.5); (0.5 < z < 1); (1 < z < 1.5); (1.5 < z < 2.5). The vertical error bars show the interpercentile range containing 68% of the sources.