Modeling and experimental studies of Ga1-xInxP growth in the Planetary Reactor(R) are presented and the mechanisms governing growth rate and compositional uniformity are identified. Reaction rate constants for the kinetically limited formation of wall deposits in this specific reactor are determined and included in the computational model. Several types of the Planetary Reactor are compared to each other. The reasons for the non-unity group III solid-vapor distribution coefficient of Ga1-xInxP are analyzed.