  We present interferometric observations of six O-type stars that were made
with the Precision Astronomical Visible Observations (PAVO) beam combiner at
the Center for High Angular Resolution Astronomy (CHARA) Array. The
observations include multiple brackets for three targets, $\lambda$~Ori~A,
$\zeta$~Oph, and 10~Lac, but there are only preliminary, single observations of
the other three stars, $\xi$~Per, $\alpha$~Cam, and $\zeta$~Ori~A. The stellar
angular diameters range from 0.55 milliarcsec for $\zeta$~Ori~A down to 0.11
mas for 10~Lac, the smallest star yet resolved with the CHARA Array. The
rotational oblateness of the rapidly rotating star $\zeta$ Oph is directly
measured for the first time. We assembled ultraviolet to infrared flux
measurements for these stars, and then derived angular diameters and reddening
estimates using model atmospheres and an effective temperature set by published
results from analysis of the line spectrum. The model-based angular diameters
are in good agreement with observed angular diameters. We also present
estimates for the effective temperatures of these stars derived by setting the
interferometric angular size and fitting the spectrophotometry.
