A finite element analysis (FEA) computer program was used to model the hydraulic characteristics and to predict the corresponding residence time distribution (RTD) curves for four full-scale ozone contactors with hydraulic capacities ranging from 14.5 to 394 m3/min (5.5 to 150 mgd). On average, model predictions for contactor efficiency (T10/HDT) were within 7.9% of actual test values. The Metropolitan Water District of Southern California (Metropolitan) is using the finite element program as a design tool to optimize the hydraulics of future ozone contactors. For one template model, results from several optimization runs are presented which confirm that T10/HDT increases with increasing depth-to-length (D/L) ratio and which indicate that by adding two features, vanes or wall foils, the T10/HDT is improved from 0.63 to 0.68 or to 0.66, respectively. Results from the template model also indicate that the T10/HDT is unchanged with the addition of a single configuration of comer fillets.