What does API gravity measure in petroleum liquids?

API gravity is a measure of how heavy or light petroleum liquid is in comparison to water. It is calculated using the specific gravity of the liquid, with a higher API gravity indicating a lighter oil that floats on water, while a lower API gravity suggests a heavier oil that sinks. This measurement is crucial in the petroleum industry, as it helps determine the quality of crude oil and its suitability for refining processes.

The other options do not accurately reflect what API gravity represents. For example, temperature, production costs, and refinement duration are not related to the concept of API gravity, which specifically focuses on the density of the oil in relation to water. Understanding API gravity allows professionals in the field to make informed decisions regarding oil exploration, production, and refining processes.