CO spectral line energy distributions of the ULIRGs in our sample. The blue circles with the error bars are the velocity-integrated line fluxes in units of Jy km s⁻¹. The dotted gray lines show the thermalized, optically thick limit (in all lines), SLED profiles, normalized to the CO(2−1) transition (which is the lowest-J CO transition that is available for all sources). The source IDs are reported on the top-left corner of each panel.