Process for sepg. one or more permeable component(s) from one or more less permeable component(s) in a feed stream (F1) involves: (a) introducing the feedstream (F1) into first membrane sepn. module (M1) comprising a high pressure side sepd. from a low pressure side by a semipermeable membrane, the membrane being selective for permeation of the more permeable component(s), and feedstream (F1) being more specifically introduced into the low pressure side of (M1).    (b) Withdrawing first permeate stream (P1) which is enriched in the more permeable component(s) of feedstream (F1) from the low pressure side of (M1).    (c) Compressing first permeate stream (P1) in compressor (C1) and introducing it into the high pressure side of second membrane sepn. module (M2), which comprises a high pressure side sepd. from a low pressure side by a semipermeable membrane which is selective for the permeation of the more permeable component(s).    (d) Withdrawing second permeate stream (P2), which is further enriched in the more permeable component(s), from the low pressure side of (M2) and recovering it as a first prod. stream.    (e) Withdrawing first nonpermeate stream (NP1), which is enriched in the less permeable component(s), from the high pressure side of (M2) and introducing it into the high pressure side of (M1); and    (f) withdrawing second nonpermeate stream (NP2) which is further enriched in less permeable component(s) from high pressure side of (M1) as a second prod. stream.    Pref. steps (a-f) are operated as a continuous cycle.    USE/ADVANTAGE -   Low pressure feed membrane sepn. process of one or more, more permeable components from one or more, less permeable components in a feed stream, more partic. sepn. where the feedstream is a mixt. of hydrogen as the one or more permeable component(s), and carbon monoxide, carbon dioxide, methane or nitrogen as the one or more less permeable component(s); nitrogen as the one or more permeable component(s) and methane as the one or more less permeable component(s); and carbon dioxide as the one or more permeable component(s) and nitrogen, oxygen and argon as the one or more less permeable component(s). Computer simulation of the membrane sepn. efficiency of this invention compared to the prior art for sepg. a hydrogen and carbon dioxide mixt. in a feedstream was performed. This invention had 4% and 5% respective advantages in energy efficiency and membrane area over the prior art.