Although membrane is efficient in bulk removal of acid gas, it is very difficult to meet stringent specification of H2S less than 4 ppm because partial pressure of acid gas in the retentate stream near the outlet is already low, which means driving force is small. To tackle this challenge, a few researchers attempted to use both amine absorption and membrane processes together, called membrane-absorption hybrid (MAH) process. Mckee et al. (1991) employed a single stage MAH process for acid gas removal from NG, with feed flow rate of 40 MMSCFD, inlet pressure of 1000 psia and 16 mol% CO2; their results suggest that, for these feed conditions, MAH process has a lower processing cost over both membrane and amine absorption processes. Bhide et al. (1998) employed a three-stage MAH process to purify two feeds (one with H2S and another without H2S), and compared its performance with that of both membrane and absorption processes. For feed without H2S, the best solution was membrane separation, whereas the optimal solution for feed with H2S depends on acid gas partial pressure, feed flow rate and pressure. The best solution for feed with 25 mol% CO2, 1 mol% H2S and flow rate of 35 MMSCFD at 800 psia, was the hybrid process. However, there are two limitations in the study of Bhide et al. (1998); firstly, only three-stage membrane configu-ration was considered for hybridization with absorption process; secondly, it is not clear whether their processes were rigorously simulated using a commercial simulator. All the above studies on MAH process are from the perspective of grass-roots design.