A kinetic model of mixed immobilized lipase (MIL) and co-immobilized lipase (CIL) systems was investigated by calculating the kinetic parameters based on the reaction mechanisms for lipase-catalyzed transesterification of soybean oil and methyl alcohol. The kinetic parameters were assessed under atmospheric and supercritical fluid conditions. Although the CIL system had a higher initial reaction rate, the effect of substrate inhibition by methanol was higher than that in the MIL system. The initial reaction rate of MIL and CIL decreased under atmospheric conditions as the methanol concentration increased. However, the initial reaction rate of MIL and CIL increased until methanol concentration increased to twice that of oil under the supercritical fluid condition. As a result, the inhibition effect by methanol was identified through a kinetic analysis. A simulated model can be used to predict the optimal conditions for biodiesel production under atmospheric and supercritical conditions.