The relationships between stellar mass (left panels) and gas fraction (right panels) with oxygen abundance (upper panels) and residual oxygen abundance (lower panels) obtained from the best polynomial fit (solid black line in the upper left panel). Dividing the sample by Hi content demonstrates that gas content is anti-correlated with metallicity for Hi normal galaxies (blue open circles). Furthermore Hi deficient systems (red solid circles) are preferentially found at higher metallicities. Such trends remain when eliminating the stellar mass dependency.