New optical oxygen sensors based on the luminescence intensities of four different europium(III) complexes, ((1, 10-phenanthroline)tris(thenoyltrifluoroacetonato)europium(III) complex ([Eu(tta)(3)phen]), tris(thenoyltrifluoroacetonato)europium(III) dihydrate ([Eu(tta)(3)] . 2H(2)O)), tris(1,1,1-trifluoro-5.5-dimethyl-2A-hexanedionato)europium(III)complex ([Eu(pta)(3)] . 2H(2)O) and tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionato) complex ([Eu(fod)(3)]. 2H(2)O)) immobilized in poly(styrene-co-2,2.2-trifluoroethyl methacrylate) (poly-(styrene-co-TFEM)) films were developed. The luminescence intensity of the europium(III) complex films decreased with increasing the oxygen concentration. Stern-Volmer plots of the europium(III) complex films exhibited considerable linearity. The K-SV values of [Eu(ttt)(3)phen]. [Eu(tta)(3)]. 2H(2)O, [Eu(pta)(3)]. 2H(2)O and [Eu(fod)(3)]. 2H(2)O in films were estimated to be 0.015, 0.005, 0.002 and 0.003 %(-1) respectively. The large K-SV value of the [Eu(tta)(3)phen] film was obtained compared with the other europium(III) complexes. The response times of the europium(III) complex films are 6.7 s for [Eu(tta),phen], 6.7 s for [Eu(tta)(3)phen]. 2H(2)O, 6.6 s for [Eu(tta)(3)]. 2H(2)O and 7.6 s for [Eu(fod)(3)]. 2H(2)O on going from argon to oxygen and 7.0 s for [Eu(tta)(3)phen].7.5 s for [Eu(tta)(3)]. 2H(2)O, 8.1 s for [Eu(pta)(3)]. 2H(2)O and 8.6 s for [Eu(fod)(3)]. 2H(2)O on going from oxygen to argon, respectively. A highly sensitive oxygen sensor using [Eu(tta)(3)phen] immobilized in poly-(styrene-co-TFEM) film has been developed.