We analyse C^18^O (J=3-2) data from a sample of 99 infrared (IR)-bright massive young stellar objects (MYSOs) and compact HII regions that were identified as potential molecular-outflow sources in the Red MSX Source survey. We extract a distance-limited (D<6kpc) sample shown to be representative of star formation covering the transition between the source types. At the spatial resolution probed, Larson-like relationships are found for these cores, though the alternative explanation, that Larson's relations arise where surface-density-limited samples are considered, is also consistent with our data. There are no significant differences found between source properties for the MYSOs and HII regions, suggesting that the core properties are established prior to the formation of massive stars, which subsequently have little impact at the later evolutionary stages investigated. There is a strong correlation between dust-continuum and C^18^O-gas masses, supporting the interpretation that both trace the same material in these IR-bright sources. A clear linear relationship is seen between the independently established core masses and luminosities. The position of MYSOs and compact HII regions in the mass-luminosity plane is consistent with the luminosity expected from the most massive protostar in the cluster when using an ~40 percent star formation efficiency and indicates that they are at a similar evolutionary stage, near the end of the accretion phase.

Cone search capability for table J/MNRAS/452/637/table1 (Source parameters for all objects in the sample, taken from the RMS survey online archive)