Two multicomponent models for spiral-wound gas permeators are proposed. The basic transport model is derived from fundamental material balances and permeation relations that account for permeate-side pressure variations. The resulting model consists of a set of nonlinear differential-algebraic-integral equations with mixed boundary conditions, as well as an implicit expression for the local feed-side flow rate. The approximate model is derived from the basic model by assuming the residue flow rate is constant in the direction of bulk permeate flow. This assumption yields a set of nonlinear algebraic equations which can be solved very efficiently and reliably. The two models are compared for the separation of CO2 from hydrocarbons in a four-component mixture, as well as the separation of an eight-component mixture. The models show close agreement for a wide range of operating conditions. An estimation technique for determining uncertain/unknown model parameters from experimental data also is proposed. The technique is successfully applied to data for a multicomponent mixture containing CO2 and CH4.