US Quart (qt)
The US quart, symbol qt, equals 1/4 of a US gallon, or about 0.946 liters. Originating from English quart measurements, it was standardized in the US system in the 19th century. Quart is frequently used in American cooking, grocery packaging, and automotive fluids. While less common internationally due to the adoption of the metric system, the quart remains an important household and commercial measure in the United States.
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.