We present recent results from our ongoing survey of CO in transitional disks around Herbig Ae/Be stars. High-resolution spectroscopy of ro-vibrational CO emission provides unrivaled views of the distribution of gas in disks and neatly complements studies of the dusty content and structure of disks to emerge from Spitzer and MIR ground-based instruments. CO is well suited to probing the inner, planet-forming regions of disks because it is relatively stable and becomes self-shielding at column densities as low as 1014 cm2. In this talk we will present results from our modeling of UV 64258 CO in disks around HAeBe stars and highlight what the data tell us about the heating mechanisms of molecular gas in disks. We will also discuss the implications various excitation mechanisms have on the apparent abundance of CO isotopomers such as 13CO and C18O. Finally, we will present constraints on the settling of dust in transitional disks as inferred from modeling the gaseous emission.
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