USCG Facility Inspector Practice Test

In this context, the important fact is the standard volume of an oil barrel. In U.S. practice, one barrel is defined as 42 U.S. gallons. This definition is used everywhere in the petroleum industry for refining, shipping, storage, and regulatory calculations, so it’s the value you apply when converting barrels to gallons in inspections and related tasks. Therefore, one barrel equals 42 gallons.

The other numbers correspond to different containers or contexts (for example, 55 gallons is a common drum size, not a barrel; 31 gallons is a beer barrel; 128 gallons isn’t a standard barrel size), so they don’t apply here.