While oil and petroleum often appear interchangeable, their meanings differ slightly. Petroleum means a broad category of products including crude oil and other by-products. Crude oil is a technical term, referring to a hydrocarbon blend that is a liquid both underground and at the surface, according to the EIA.
Crude oil is a type of petroleum, as are some other hydrocarbon liquid mixtures, such as unfinished oils, lease condensate, natural gas, plant liquids and other products that come from processing crude oil. Crude oil can also have gaseous hydrocarbons, when underground, that enter a liquid phase when they come up from the oil well. Other substances that can appear in crude oil include drip gases, sulfur, metals (that come up with the oil during production) and liquid hydrocarbons that are by-products from oil shale, gilsonite, oil sands and tar sands.
However, crude oil does not include liquid products that come from processing plants that handle natural gas. Crude oil itself goes through refining to create such products as gasoline, jet and diesel fuels, heating oil, asphalt, lubricating materials, butane, propane and ethane, as well as a wide variety of other by-products that have usable chemical or energy content, as stated by the EIA.