The Hi mass fraction of the GASS sample is plotted here as a function of stellar mass, stellar mass surface density, concentration index, and observed NUV − r color. Red circles and green triangles represent detections and non-detections, respectively. For comparison, we also show the full set of ALFALFA galaxies meeting the GASS selection criteria that have been cataloged to date (gray). The dashed line on the top-left panel indicates the Hi detection limit of GASS. Dotted lines in each panel are linear fits to the Hi detections only.