Wind-momentum–luminosity relationship (WLR) for our sample compared with theoretical predictions from Vink et al. (2001) for the metallicities of the Milky Way and the Magellanic Clouds. Stars with upper limits on log Q (hence D_mom) are plotted with open symbols, and those analysed using the nitrogen lines are plotted with diamonds. Typical uncertainties are shown in the upper left corner, and the vertical dashed line indicates log L/L_⊙ = 5.1. Results from Bouret et al. (2003), Martins et al. (2005), and Mokiem et al. (2007a) for their samples of O dwarfs in the SMC, MW, and LMC O, respectively, are plotted in red; the use of clumped (“cl.”) or unclumped (“uncl.”) wind models in each work is also indicated in the legend.