A steady-state model is presented for a hollow fibre liquid membrane extractor which describes the mass transfer performance as a function of phase flows, geometry and system physical properties. The model is compared with the experimental results for Cr(VI) extraction with a tertiary amine carrier. Shell side mass transfer correlations, developed primarily for gas-liquid membrane contactors, are also incorporated into the model and compared. This model is subsequently used to optimise both operating and design parameters for maximum mass flux in hollow fibre liquid membranes.