What Is Sweet Crude?

Sweet crude refers to crude oil that is extracted that is found to contain very low amounts of sulfur. It is considered a valuable and efficient source of crude oil due to the fact that sulfur lowers the yield of various refined petroleum products such as gasoline, diesel fuel, and even plastics.

Sweet crude can be contrasted with the less desirable sour crude, which has a high level of sulfur content.

Key Takeaways

  • Sweet crude is a type of crude oil classified by its low sulfur content.
  • When combined with low density, sweet crude is a highly sought after type of oil which commands a high price, known as light sweet crude.
  • In North America, a popular example of sweet crude oil is the West Texas Intermediate (WTI) crude oil, which is actively traded on the New York Mercantile Exchange (NYMEX).

How Sweet Crude Works

Crude oil is composed primarily of carbon and hydrogen, which represent about 85% and 12% of its chemistry, respectively. The remaining elements consist of sulfur, oxygen, nitrogen, and helium. Depending on the composition of the trace elements, the process for refining crude oil can vary substantially in terms of the amount of residual byproduct—or “residuum”—left over after refining. 

Oil is easiest to work with if its sulfur content is kept very low. To help produce an industry-standard definition of this high-quality oil, the NYMEX exchange has put forward a definition of crude sweet oil, stating that it must possess no more than 0.42% sulfur content. 

Although today precise techniques are available to assess the sulfur content of a sample of oil, past generations of oil prospectors would deduce a sample’s sulfur content by literally tasting it themselves. If the sample tasted vaguely sweet and had a pleasant smell, that meant it was low in sulfur. A sour taste with the smell of rotten eggs indicated a high sulfur content. It is through this old testing method that the terms "sweet crude" and "sour crude" came to be.

Other Considerations

In addition to controlling sulfur content, the quality of crude oil is also affected by its density. According to the density standards set out by the American Petroleum Institute (API), crude oil can also be identified as “light” or “heavy” depending on its density relative to water. For example, crude oil with a density equal to that of water is defined as having an “API Gravity” of 10. 

The API’s density scale is inverted, meaning that oil with an API Gravity greater than 10 will float on water and be called “light crude”. Conversely, oil with an API Gravity below 10 will sink in water and be known as “heavy crude”. Although not all light crude is sweet, most heavy crude is sour because it typically contains large amounts of sulfur as well as metals such as nickel. Low-density (or “light”) oil is desirable because it is easier to refine, distill, and transport.

Real World Example of Sweet Crude

Combining these elements together, we can see that the most desirable type of crude oil is light sweet crude. This is because it is highly efficient, leaving minimal residue in its refinement process while also being easy to distill and transport due to its low density.

Perhaps the most famous example of light sweet crude oil is known as West Texas Intermediate, or WTI crude oil, which is both lighter and sweeter than other major types of oil, such as Brent crude oil and Dubai crude oil. Its popularity in North America is due in part to the fact that it is produced and refined in North America, while also being actively traded on commodity futures markets such as the NYMEX.