The average density for motor oil is 0.865 grams per cubic centimeter, which is about 7.2 pounds per gallon. The density of the oil depends on the formula of motor oil used and the temperature of the oil.
Different formulas of motor oil are used for different applications and have different densities. For example, SAE 15W-40 motor oil at 32 degrees Fahrenheit weighs 7.4 pounds per gallon, while SAE 0W-30 motor oil at 212 degrees Fahrenheit weighs 6.7 pounds per gallon. The numbers that denote the type of oil refer to the SAE testing standards that motor oils undergo. The first number, if an oil has one, is the viscosity rating at cold temperatures, and the second (or perhaps only) number is the viscosity rating at 212 degrees Fahrenheit.