Blackbody cavities are commonly used in calibration of optical sensors; that is, they provoke an instrument response to a known incident flux. The so-called cavity effect produces an effective emissivity near unity so that, if a uniform temperature distribution is maintained across the cavity wall, the flux exiting the cavity approaches that of a blackbody at that temperature. The effort described here employs Monte Carlo ray-trace (MCRT) models to simulate radiation within a blackbody cavity in order to define the spatial and angular distributions of exiting flux. These models may be used to evaluate the suitability of various cavity geometries for the calibration of radiometers. The sensitivity of exiting flux properties to variations of interior surface properties and temperature may also be evaluated. Described is an effort to develop a tool that can be used to enhance the design and utilization of blackbody cavities as a calibration source.