Process design and optimization methodology for high pressure membrane removal of CO2 from natural gas was developed. An approximate model based on plasticization pressure and permeability parameters at plasticization was proposed for quick evaluation of membrane materials for the high pressure operation. The model was derived by applying the partial immobilization assumption to the fundamental model of solution - diffusion mechanism along with a modified upper-bound curve. About ninety membranes obtained from literature were used to illustrate this methodology. The best three were selected for detailed process modeling and optimization. Process optimization was achieved via non-linear programming constraint optimization model. Gas processing cost was used as the objective function, while plasticization pressure and the CO2 concentration in the feed were used as the constraints. Membrane of 6FDA-durene had the lowest annual gas processing cost while 6FDA-DAM : DABA 2 : 1 had the highest optimum product purity.