UK Barrels
A UK barrel is 36 imperial gallons (not to be confused with American gallons), about 163.659 liters or 0.163659 cubic meters. It is based on the traditional wine barrel used in the United Kingdom.
US liquid gallons
A US liquid gallon is a volume measurement used in the United States for liquids such as water, gasoline, and milk. One US liquid gallon is about 3.78541 liters. A standard bathtub is about 80 gallons of water and a car gas tank can hold anywhere between 12 and 20 gallons of gas.