Cubic Millimeters
Cubic millimeters are volume units in the metric system. A cubic millimeter is a unit of volume equal to the volume of a cube with sides measuring one millimeter each. It is a very small unit of volume commonly used to measure tiny amounts of liquids or solids. For example, a single drop of water may have a volume of approximately 50 cubic millimeters.
US oil barrels
A US oil barrel, also known as a petroleum barrel, is a volume unit used in the oil and gas industry to measure crude oil or liquid petroleum gas (LPG). One US oil barrel is 42 US gallons or about 159 liters.