It was found that the measured FER parameters generally showed highly similar results with those obtained from FluidscanQ1000 and titration methods. The FER parameter seems to increase relatively earlier (in 450 h) than others, providing an early warning of oil oxidation, since FER parameter is more integrated one, which reflects aromatic composition and polarity of the oil. It is believed that the FER parameter shift with the oil oxidation precedes the increase in the acid number of the oil sample. It is worth while noting that the fluorescence of oxidized oils relates to energy transition phenomena in the p orbitals of C@C bonds of organic matters, while the acid number of oil relates to the formation of acidic matters to be titrated by the added KOH solution. This result suggests that the proposed FER sensor could be an effective indicator of the oil oxidation level.