Types of Crude Oil: Heavy vs Light, Sweet vs Sour, and TAN count

Crude Oil Samples

What is Crude Oil?

What are we referring to when we talk about oil?

Crude oil is a black liquid found in geological formations. It is a fossil fuel, which means it is formed from dead organisms that are buried under intense heat and pressure.

But not all crudes are alike. There are three primary qualities that differentiate one oil from another: Weight, Sweetness, and TAN count.

Weight of Crude Oil

Heavy crude oil evaporates slowly and contains material that will be used to make heavy products like asphalt. The standard unit of measurement is API Gravity.

Lower and Higher API Gravity Crude Oil Samples

Sweetness of Crude Oil

You’ve probably heard people referencing “sweet” and “sour” oil.

What makes a particular crude sweet or sour is the amount of sulfur it contains. Sweet crude has very low levels of sulfur, well under 1%. Sour crude has as much as 1-2% of sulfur.

Midstream companies and refiners that transport, store, and process sour oil know they need extra treating capabilities to take out the sulfur and sweeten the product.

TAN Count of Crude Oil

TAN stands for “Total Acid Number.” The TAN count of oil is a measure of how corrosive it is.

If a crude has a high TAN number, you’re going to need different metallurgy so your processes can handle that corrosivity and keep the crude in the pipe.

Companies use a test called an assay get a full chemical breakdown of what is in a barrel of oil. The ideal oil is light and sweet with a low TAN count, while the harder to process oil is heavy and sour with a high TAN count.

Benchmark Crude Oils: OPEC, WTI, and Brent

There are over one hundred different crude oils traded on the market today. These oils are typically labeled by the region they come from, and they have a specific chemical makeup

Density and Sulfur Content of Selected Crude Oils

Graph from EIA

The three most well known regional benchmark oils are WTI, Brent, and OPEC.

WTI stands for West Texas Intermediate. This is oil produced in the United States. It is typically on the lighter end of the spectrum, at an API gravity of 39.6. It is also at the sweeter end of the spectrum, with a sulfur content of 0.24%.

Brent oil comes from the Scottish Brent and Ninian Systems located in the North Sea. This oil is also light and sweet, with an API gravity of 38.3 and a sulfur content of 0.37%.

OPEC stands for “Organization of Petroleum Exporting Countries.” It is a collective group of seven different crude oils from Algeria, Saudi Arabia, Nigeria, Dubai, Indonesia, Venezuela, and the Mexican Isthmus. The oil from these regions is typically on the heavier and sour end of the spectrum.

While logistics also play a role, typically the lighter and sweeter an oil is, the more expensive it’s going to be.


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Mark Anderson serves as a Product and Applications Trainer at Kimray.