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 Inch (in³)
The cubic inch, symbol in³, is a US customary and imperial unit representing the volume of a cube with each side one inch in length. Its use dates back centuries in English measurement systems. Today, it is particularly significant in the automotive industry, where it historically defined engine displacement before metric liters became common. One cubic inch equals 16.387 milliliters, making it a small but practical unit for precision engineering, manufacturing, and certain niche applications.