a method for the quantitative determination of dissolved oxygen in a liquid fuel includes the steps of doping a sample of the fuel with a preselected concentration of a probe material including a luminophor which exhibits luminescence of wavelength which is quenched by oxygen dissolved in the fuel , illuminating the fuel with light from a coherent light source , such as a laser , of a wavelength which induces the luminescence in the luminophor , and thereafter measuring the change with time of the luminescence from the luminophor in the fuel and determing from the change with time of the luminescence the concentration of oxygen in the fuel .