Water-oil separation is important in the oil industry, as the incorrect classification of oil can lead to losses in the production and environmental impact. This paper proposes the use of fiber Bragg grating (FBG) temperature sensor array to identify the oil in water-emulsion-oil systems, using only the temperature responses for oil classification results in operational and economic benefits. To demonstrate the possibility of using the FBG temperature sensor to classify oil level, the temperature distribution of an oil storage tank, with 2 m height and 0.8 m in diameter, is simulated using thermal distribution models. Then, the temperature effect in a 2 m long FBG array with different number and distribution of FBGs is simulated using the transfer matrix method. In each case, we extract the wavelength shift, total width at half the maximum (FWHM) and the location of the FBG in the fiber. For the oil classification, we dichotomized the fluids into oil and not oil (water and emulsion). Due to the low variability of the classes, the Random Forest algorithm was chosen for classification. Starting with 200 FBG equidistant sensors and decreasing to 6, with different distributions along the fiber. As expected, the highest accuracy occurs with the 200 FBGs array (96%). However, it was possible to classify the oil with an accuracy of 94.89% with only 8 FBGs, using Tests for Two Proportions (with a significance of 5%), the accuracy for 8 FBGs is the same of 50 FBGs.