Fog oil is a petroleum oil used to fill thermal generator smoke pots. Two grades of fog oil, SGF1 and SGF2, are used. SGF1 is the thicker of the two and has a viscosity approximately the same as SAE 40 motor oil. The viscosity of SGF2 is approximately the same as SAE 15 motor oil. Kerosene is used to dilute the fog oil filling when smoke pots are to be operated at low temperatures.