API gravity relates to which of the following properties of petroleum liquids?

• A. Color
• B. Viscosity
• C. Reactivity
• D. Density of petroleum liquids

Answer: (D)

API gravity is a measure of how heavy or light a petroleum liquid is by its density relative to water. It’s derived from the liquid’s specific gravity (density compared to water) at a standard temperature (usually 60°F). Because the API scale is defined so that higher API numbers correspond to lower density, the concept ties directly to density: a liquid with lower density (lighter) has a higher API gravity, while a denser (heavier) liquid has a lower API gravity. This is why API gravity is used to classify crudes as light, medium, or heavy, which has practical implications for processing, storage, and pricing.

Color, viscosity, and reactivity describe other properties that API gravity does not measure. Color is about appearance, viscosity is about flow resistance, and reactivity concerns chemical behavior.