Ratio of SFR and CO-inferred H₂ mass vs. relative metallicity as described in the text, including our data and data from the literature (COLDGASS: Huang & Kauffmann 2014; Schruba et al. 2012; Bothwell et al. 2014). As in previous figures, the open triangles for Schruba et al. (2012) correspond to their compilation of data from the literature and the filled ones to their metal-poor dwarf observations. In the left panel, M_H2 is inferred with our formulation of α_CO as a power-law dependence on O/H as described in the text; in the right panel, we use the exponentially-dependent α_CO as found by Wolfire et al. (2010), Krumholz et al. (2011). Also shown are the predictions by Krumholz et al. (2011), showing three values for total gas surface density, Σ_gas: 5 M_⊙ pc^-2, 20 M_⊙ pc^-2, and 80 M_⊙ pc^-2 indicated by dashed, dotted, and solid lines, respectively. Red color shows total gas, purple H₂, and blue CO.