Oilers/Plant Tenders (HHC) Civil Service Practice Exam 2026 - Free Oilers & Plant Tenders Practice Questions and Study Guide

The terms "heavy" and "light" in relation to oil primarily refer to oil density, which is a measure of how heavy or light a given volume of the oil is compared to an equal volume of water. In the context of crude oil, "heavy oil" is generally denser and contains a higher proportion of larger hydrocarbons, making it more viscous and difficult to pump. Conversely, "light oil" is less dense, containing a higher proportion of smaller hydrocarbons, which makes it easier to transport and refine.

While viscosity is a related concept, the distinction of "heavy" and "light" is best understood through density. Heavy oils, with higher density, also tend to be more viscous, but the primary classification is based on how they compare in weight relative to water, hence the emphasis on density. Other choices such as oil color or temperature don't accurately reflect the distinctions used in the petroleum industry when categorizing oils by their physical and chemical properties.