Abstract: Use of an oxygen sensor comprising a membrane, preferably in the form of a first tube (2), which is substantially made of zirconium dioxide and has an internal and an external coating (3, 4) of an electrically conductive, catalytic layer. On the electrically conductive, catalytic layer, a porous, preferably ceramic layer (5) is provided. The porous layer (5) is provided on the electrically conductive, catalytic layer (3), which is located at least partially within a second tube (6), made of a gas tight material. The oxygen sensor, which is part of a clamped together structure with O-rings, may be used in a method, in which the measuring gas, especially a reactive measuring gas, is supplied to the external side of the first tube (2).