Orbital period vs. I-band magnitude for target with photometry from Clark et al. (2005) or Bonanos (2007). Systems with circular orbits are plotted as filled circles, while systems with eccentric orbits are plotted with ‘×’ symbols. Black circles show X-ray sources from Paper II. Red, green, and blue points indicate spectral type, following Figs. 6 and 16. Note that the orbital period for W10 is not firm, and its I-band magnitude is estimated from its R-band magnitude of 18.516 (Bonanos 2007) under the assumption that it has the same reddening as other nearby early-B supergiants.