  We present an analysis of CO emission lines from a sample of T Tauri, Herbig
Ae/Be, and transitional disks with known inclinations, in order to study the
structure of inner disk molecular gas. We calculate CO inner radii by fitting
line profiles with a simple parameterized model. We find that, for optically
thick disks, CO inner radii are strongly correlated with the total system
luminosity (stellar plus accretion), and consistent with the dust sublimation
radius. Transitional disk inner radii show the same trend with luminosity, but
are systematically larger. Using rotation diagram fits, we derive, for
classical T Tauri disks, emitting areas consistent with a ring of width ~0.15
AU located at the CO inner radius; emitting areas for transitional disks are
systematically smaller. We also measure lower rotational temperatures for
transitional disks, and disks around Herbig Ae/Be stars, than for those around
T Tauri stars. Finally, we find that rotational temperatures are similar to, or
slightly lower than, the expected temperature of blackbody grains located at
the CO inner radius, in contrast to expectations of thermal decoupling between
gas and dust.
