What is the unit of liquid measure that is equivalent to 42 U.S. gallons at 60°F?

The correct answer is a barrel, which is a unit of liquid measure commonly used in the oil and petroleum industry. A standard barrel, specifically referred to as a petroleum barrel, is defined as 42 U.S. gallons at 60°F. This unit is important as it provides a consistent measure for production and transportation quantities in the energy sector.

The presence of other options may lead to confusion; however, a drum typically holds around 55 gallons and is not equivalent to the 42-gallon specification of a barrel. A tank usually refers to a larger storage container, which does not have a specific measurement equivalent to the 42 U.S. gallons. Similarly, a cask is a barrel-like container used for storing liquids, often in the beverage industry, but it does not have a defined measurement that matches the 42-gallon volume specifically. Thus, while all these terms relate to containers for liquids, only the barrel has the precise definition that corresponds to 42 U.S. gallons under standard conditions.