(a) CO luminosity vs. ﹩S_{\mathrm{sep}\,}﹩ for 50 LIG mergers. A strong correlation holds for the less luminous LIGs (﹩L_{\mathrm{IR}\,}\lesssim 10^{12}\,L_{\odot }﹩, filled circles with line fit), which resemble the volume‐limited complete sample, whereas no correlation holds for the ultraluminous ones (ULIGs, open circles). (b) No correlation holds between ﹩L_{\mathrm{IR}\,}﹩ and ﹩S_{\mathrm{sep}\,}﹩ for either ULIGs or LIGs. (c) The anticorrelation between ﹩L_{\mathrm{IR}\,}/ M﹩(H₂), the measure of star formation efficiency, and ﹩S_{\mathrm{sep}\,}﹩ suggests the enhanced star formation efficiency of late‐stage mergers. We use the same conversion factor from ﹩L_{\mathrm{CO}\,}﹩ to molecular gas mass even though there is evidence that ULIGs require a smaller conversion factor (S97; DS98). The fit is for LIGs.