Which option best defines ullage?

• A. The weight of the cargo
• B. The volume of the liquid
• C. The temperature of the liquid
• D. The distance from liquid surface to top of tank

Answer: (D)

Ullage is the empty space in a cargo tank, measured as the distance from the surface of the liquid to the top of the tank. This headspace matters because it indicates how much liquid remains and how much space is available for vapor, which is important for accurate quantity gauging, safe operation to avoid overfilling, and managing vapors and pressure. The other options describe different properties: the weight of the cargo is a measure of mass, the volume of the liquid is how much liquid is present, and the temperature of the liquid is a separate property affecting density and behavior, none of which define the empty space in the tank.