Continuous separation of bidisperse suspensions containing particles of significantly different size and density in a vertical settler was examined. The effects of the feed total solids volume fraction, composition, and flow rate on the performance of the settler were investigated. For feed total solids volume fractions less than 0.1, a kinematic model based on the Patwardhan and Tien (1985) expression for relative velocity was found to predict the experimental measurements fairly well over a wide range of parameters. For feed total solids volume fractions greater than 0.2, a strong local instability was observed in the settler. This local instability significantly improved the performance of the settler in some cases.