Velocity-integrated CO line luminosity of 11−10 and 16−15 transitions versus source bolometric luminosity from low- to high-mass star-forming regions. The dashed lines show a linear fit obtained using only the sources from our study, which are shown in blue empty circles. Blue stars show observations of other high-mass protostars from Karska et al. (2014), Indriolo et al. (2017), and Kaźmierczak-Barthel et al. (2014); orange squares present emission from intermediate-mass objects (Matuszak et al. 2015); and red triangles show data for Class 0 protostars (Kristensen et al. 2017).