Abstract: Perfluoropolyether compounds and mixtures thereof having the formula:A--O--(C.sub.3 F.sub.6 O).sub.P --(CF.sub.2 O).sub.Q --(C.sub.2 F.sub.4 O).sub.R --CF(Z)--CO--N(R)Arwherein the perfluoroalkyleneoxy groups are randomly distributed and A is a perfluoroalkyl group or a --CF(Z)--CO--N(R)Ar group; P, Q and R are zero but not simultaneously or numbers from 1 to 100, the sum of P, Q and R being 3 to 200; Z is a fluorine atom or a CF.sub.3 group; Ar is an aryl group; and R is hydrogen, alkyl, alkyl-aryl or an aryl group.These compounds are excellent stabilizers for perfluoropolyether fluids of the formula:X--O--(C.sub.3 F.sub.6 O).sub.P --(CF.sub.2 O).sub.q --(C.sub.2 F.sub.4 O).sub.r --Ywherein p, q and r are each zero or numbers from 1 to 100, the sum of p, q and r being 6 to 200, and X and Y are the same or different and are perfluoroalkyl groups having 1 to 3 carbon atoms.