Crude oil is a naturally occurring, unrefined petroleum product composed of hydrocarbon deposits and other organic materials. Crude oil can be refined to produce usable products such as gasoline, diesel and various forms of petrochemicals. It is a nonrenewable resource, also known as a fossil fuel, which means that it can't be replaced naturally at the rate we consume it and is therefore a limited resource.
Many types of crude oil are produced around the world. The market value of an individual crude stream reflects its quality characteristics. Two of the most important quality characteristics are density and sulfur content. Density ranges from light to heavy, while sulfur content is characterized as sweet or sour. The crude oils represented in the chart are a selection of some of the crude oils marketed in various parts of the world.
Crude oils that are light (higher degrees of API gravity, or lower density) and sweet (low sulfur content) are usually priced higher than heavy, sour crude oils. This is partly because gasoline and diesel fuel, which typically sell at a significant premium to residual fuel oil and other "bottom of the barrel" products, can usually be more easily and cheaply produced using light, sweet crude oil. The light sweet grades are desirable because they can be processed with far less sophisticated and energy-intensive processes/refineries. The figure shows select crude types from around the world with their corresponding sulfur content and density characteristics.