Left panel: star formation rate against H₂ mass. Virgo SFDs (blue dots) are compared to the HRS spiral (grey squares) and irregular-peculiar (red triangles) galaxies. Hi-deficient galaxies are indicated with empty symbols, and blue arrows are Virgo dwarf upper limits. The solid line shows the best-fit relation. Dotted lines indicate constant molecular gas depletion timescales of 0.1, 1, and 10 Gyr. Central panel: star formation rate against Hi mass. Symbols are the same as in the left panel. The solid line shows the best-fit relation. Dotted lines indicate constant atomic gas depletion timescales of 1, 5, and 10 Gyr. Right panel: star formation rate against total gas mass (M_H2 + M_HI). Symbols are the same as in the left panel. The solid line shows the best-fit relation. Total gas depletion timescales of 1, 5, and 10 Gyr are also overlaid. Coefficients of the best-fit relations are given in Table 4.