US Gallon (gal)
The US gallon, denoted as gal, is a unit of volume that equals approximately 3.785 liters. It comes from old English wine gallons and became official in the US in the 1800s. People in the US still use it extensively for fuel, beverages, and cooking. The US gallon is smaller than the British one, which leads to different numbers in global trade and when comparing fuel use. Although most countries use metric units, the US gallon remains a significant part of US life.
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.