(WO9511738-A1)      A membrane process for treating a gas stream contg. H2S, CO2 and CH4 comprises: (a) passing a feed stream contg. CO2 and H2S through a membrane unit; and (b) withdrawing from the unit a residue stream contg. CO9 in a concn. no greater than 3 vol.% and H2S in a concn. no greater than 20 ppm. The feed stream contains CO2 in a concn. less than 3% to less than 10% and H2S in a concn. more than 10 ppm to more than 300 ppm. The lower end of the CO2 range corresponds to the lower end of the H2S range (less than 3% CO2; greater than 10 ppm H2S) and the upper end of the CO2 range corresponds to that of the H2S range (less than 10% CO2; greater than 300 ppm H)2S). The membrane unit has a membrane having a selectivity for H2S over CH2 of at least 35 and a selectivity for CO2 over CH4 of at least 12. Selectivity is measured with a mixed gas stream contg. at least H2S, CO2 and CH4 at a feed pressure of at least 500 psig.    Also claimed are the following: (1) a process in which the feed stream contains CO2 in a concn. less than 10% to less than 20% and H2S in concn. more than 330 ppm to more than 600 ppm with lower and upper ends of the CO2 range corresponding to those of the H2S range; (2) a process which the feed stream contains CO2 in a concn. less than 20% to less than 40% and H2S in a concn. more than 600 ppm to more than 1%; and (3) a process in which a feed stream of CO2, H2S and CH4 is passed through two membrane units arranged in series (see CLAIMED PROCESS).    USE -   The process is used for removing H2S and CO2 from gas streams such as natural gas.    ADVANTAGE -   As the membrane has a higher selectivity for H2S and CH4, the membrane treatment can be applied efficiently to gas streams having high concns. of H2S, the processes can handle gas streams of high relative humidity. A natural gas stream can be brought into pipeline specifications for CO2, H2S and water vapour with a single membrane treatment. Over-processing of the gas stream is avoided, there is greater flexibility to adjust membrane operating and performance parameters by provision of two types of membranes. The process can be optimised by calculating the appropriate membrane mix to use.