Barrel (oil, bbl)
The oil barrel, symbol bbl, is a unit of volume commonly used in the petroleum industry. Its origins date back to the mid-19th century, when the American oil industry adopted the wooden barrel as a standard for storage and transportation. In 1866, the barrel was officially set at 42 US gallons (about 159 liters) to unify trade and pricing. Although physical barrels are no longer used, the “barrel” remains a widely recognized standard for oil production, consumption, and trading. The oil barrel is commonly referenced in discussions of energy, economics, and industrial development as a non-metric unit of volume.
Cubic Centimeter (cm³ or cc)
A cubic centimeter (cm³/cc) is a metric volume unit equivalent to one milliliter. Established with the metric system in the 1700s, it is frequently employed in scientific, engineering, and medical settings to measure small quantities accurately. The abbreviation “cc” is particularly prevalent in medical prescriptions for liquids and in the automotive field for specifying engine size. Since it matches the volume of a milliliter, the cubic centimeter is easily compatible with the rest of the metric system while remaining important in specialized applications.