Abstract: An apparatus and non-invasive method of measuring oxygen by exciting a luminescent compound disposed in a container and then measuring the intensity of the light emitted by the excited luminescent compound as it relaxes to the ground state. A plot of emission intensity as a function of time results in an exponential decay curve the area of which is inversely proportional to the oxygen concentration. The oxygen concentration can be determined over a wide temperature range by measuring the temperature of the container and the emission intensity and then applying the following equation: [O2]=(ATa(T)2+BTa(T)+CTa)(tau)2+(ATb(T)2+BTb(T)+CTb)(tau)+(ATc(T)2+BTc(T)+CTc) T is the measured temperature; tau is the area of the exponential decay curve; and ATa, BTa, CTa, ATb, BTb, CTb, ATc, BTc, and CTc are coefficients that are specific to the luminescent compound being examined.