In order to understand the basic characteristics of the gas-phase mass-transfer coefficient (kg) in a small silicon Czochralski (Cz) furnace, a very crude model was proposed and the results were correlated by the Sherwood number as a function of Reynolds number. It was confirmed that by installing a gas guide in the hot zone, the mass transfer coefficient was significantly enhanced. A set of global analyses of small Cz furnaces was conducted with different values of diffusivity of SiO in the gas phase (DSiO) and of oxygen in the melt phase (DO) in order to elucidate which rate process controls the average oxygen concentration ([O]ave) in the grown crystal. These simulations revealed that in these small Cz furnaces, [O]ave is dependent on the gas phase mass transfer rate and melt flow patterns. A decrease in DSiO causes an increase in [O]ave. An increase in DO tends to increase [O]ave slightly in most cases.