A new oxygen/nitrogen gas concentration sensor is described in this paper. This new sensor is based on the permselectivity of a membrane element. It is especially suited for the very low price market to determine the concentration of binary or pseudo-binary gas mixtures in the 0-100% range. The sensor is made of a permselective membrane module whose permeate stream is linked to a needle valve. The feed composition is related to the permeate build-up pressure, measured using a pressure transducer. Poly(dimethylsiloxane) (PDMS) and poly (etherimide) (PEI) hollow fiber membranes were tested. The response curves for both membranes at different temperatures display a quasi-linear behavior. The PDMS membrane-based sensor enables continuous and rapid oxygen analysis (t(0-95%) = 50 s) with a reproducible and long-term stable signal ((k) over bar (O-2) = 2.474 x 10(-6) dm(3) (STP) s(-1x) m(-2) Pa-1, s = 0.045 x 10(-6), N = 10; (k) over bar (N-2) = 1. 173 x 10(-6) dm(3) (STP) s(-1) m(-2) Pa-1, s = 0.010 x 10(-6), N = 11) over 5.4 x 10(6) s. The absolute sensitivity of the PDMS-based sensor depends on the oxygen feed concentration ranging from 0.0329 to 0.450 MPa. A simple analytical model was developed and is presented here. Good agreement was obtained with the experimental results for both membranes. (C) 2004 Elsevier B.V. All rights reserved.