Quenching of the molecular excimer fluorescence is proposed for measuring the concentrations of an analyte. The validity of this concept is demonstrated by constructing an oxygen sensor that is based on the quenching of the pyrene excimer fluorescence. The Stern-Volmer type analysis of the quenching data obtained for the monomer and excimer fluorescence reveals that for the excimer fluorescence the oxygen quenching is 3 times faster than for the monomer quenching. Furthermore, the excimer quenching plot is linear while the monomer quenching plot shows a downward curvature. The response of a 0.1 mm thick sensing layer made out of silicone rubber is fully reversible with a response time of less than 5 sec. An empirical relation that correlates the fluorescence intensity of the two excited species to the quencher concentration is presented. This relation is suitable for exploitation in developing `ratio sensors.' Various factors contributing to improved sensor performance are discussed.