What Is a Crude Oil Assay?

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  • Written By: Mary McMahon
  • Edited By: Nancy Fann-Im
  • Last Modified Date: 04 November 2019
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A crude oil assay is an evaluation of the properties of a sample of crude oil for the benefit of refiners, traders, and other interested parties. All crude oils are not created equally, and assay results can determine the value of oil in addition to helping with plans for refining and working the oil to break it down into usable components. This can be performed at the laboratory of an oil company or by a third party organization, depending on who orders the assay and what the precise need might be.

In a crude oil assay, chemists specializing in petroleum products subject the sample to a number of tests. They determine the composition of the oil, identifying any impurities present and their concentrations. The chemists can also distill the oil to find out more about what kinds of usable components it will yield. This process can be destructive and usually requires several samples to make it possible to run a variety of tests. Tests may be repeated if there are any questions.


The crude oil assay looks at qualities of the oil when it is hot and cold, and also explores the quality of finished products like gasoline. All of this information determines the final rating of the oil, such as light sweet crude for particularly high quality oils. The better the rating, the more valuable the oil, and the more products it will be possible to make from it. For oil and gas exploration, oil assays are critical for determining where and when to drill, and for evaluating the value of a prospective investment.

Traders use the crude oil assay to find out how much to ask or pay for various oil products, while refineries rely on the assay to develop a plan for processing the oil. The goal is to extract as many useful components as possible through processes like distillation and hydrocarbon cracking. Knowing the properties of the oil ahead of time will allow the refinery to determine how it should handle the oil on delivery. It can also be critical for maintaining refinery statistics on the type of oil it processes and the average yields.

Government agencies can also use assays, where the goal is usually to determine the value of oil reserves. In addition to being useful for assessing the value of oil deposits held by the government, a crude oil assay can also be a valuable forensic tool. Oil contains markers that provide clues into its origins, making it possible to track the origins of oil no matter where it turns up. This can be important for environmental investigations or situations where governments want to avoid buying oil from embargoed or restricted regions.


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