Same as Fig. 3, but color-coded by the molecular over cold gas fraction (top), and baryonic molecular (middle) and neutral (bottom) gas fractions. The molecular gas fraction (top panel) correlates with Σ_H2 at all redshifts. The baryonic molecular fraction (middle panel) correlates with Σ_H2 at high redshifts; below z ∼ 2 this correlation weakens and is essentially carried by low-mass galaxies. The correlation between the neutral gas fraction and Σ_H2 is apparent only at z = 4. At z ≲ 2 the trend reverses, meaning this fraction decreases with increasing Σ_H2.