Gas fraction = MH₂/(M(H₂) + M_∗) versus CO luminosity, assuming the same CO-to-H₂  conversion factor α = 0.8 M_⊙ (K kms^-1 pc²)^-1. The points of the high-z samples (blue asterisks and green dots), have been continued by a dotted line joining the two extreme values of gas fraction, obtained with α = 0.8 and 4.6. We indicate these lines only for the points in the high-z samples for which the MW conversion factor was selected by the authors. All symbols are as defined in Fig. 6.