Total H i mass, M_{H I} (in M_⊙), as a function of radial velocity (in km s^-1), i.e., V_{H I} for the detections and SDSS optical values for the non-detections. Black dots represent clear NIBLES detections, gray diamonds marginal detections, and open red triangles estimated upper limit for non-detections. Excluded were all NIBLES detections which are either resolved (flag R in the tables), or definitely or probably confused by another galaxy within the telescope beam (flags C1 and C2). The relatively high estimated upper limits for non-detections are quite conservative, as they are based on the largest W₂₀ line widths measured as a function of r-band luminosity (see Sect. 4).