Casual discussions of crude oil often times make it seem as if there is only one type of crude oil for all uses. However, crude oil is actually recovered in a number of different physical and molecular states. It exists as light, medium, or heavy crude, and it may be dubbed "sweet" or "sour." These various classifications affect all aspects of the crude oil’s recovery, delivery and final use from its origin upstream, transportation through the midstream phase, and to the end user downstream. Different types of crude oil have different end usage, require various refinement techniques, and ultimately yield different quality products.
Classification Systems for Crude Oil
The petroleum industry typically classifies crude oil based on the following three ways:
Geographic Location - The geographic location of the oil field where the oil is recovered is commonly used to classify it. Thus crude oil might be called West Texas Intermediate, Brent Blend, or Dubai-Oman.
API Gravity - API gravity refers to a density scale developed and used by the American Petroleum Institute (API). API Gravity is an inverse measure of the density of petroleum and the density of water. If the crude oil has an API greater than 10 it will float on water and is thus lighter than water. If the crude oil has an API lower than 10 it will sink in water due to being heavier.
Sulfur Content - The third way crude oil is commonly classified is based on its sulfur content. If the crude contains relatively little sulfur then it is called "sweet." If it contains a large amount of sulfur then it is called "sour."
Types of Crude By API Gravity
When crude oil is classified based on its API gravity it is divided into one of the following four classifications:
- Light - Light crude oil has an API gravity of 31.1 °API or higher.
- Medium - Medium crude oil has an API gravity that ranges between 22.3 °API and 31.1 °API.
- Heavy - Heavy crude oil has an API gravity that ranges between 22.2 °API and 10 °API.
- Extra Heavy (Bitumen) - Extra heavy crude oil has an API gravity that is lower than 10 °API. Extra heavy crude oil is also commonly called “bitumen.”
Types of Crude By Sulfur Content
When crude oil is described based on its sulfur content it is designated in one of the following two ways:
Sweet - Sweet crude oil has a sulfur volume lower than 0.42%.
Sour - Sour crude oil has a sulfur volume higher than 0.50%.
The terms "sweet" and "sour" originated from the practice of nineteenth century prospectors who would literally taste or smell the crude to determine its quality. The lower sulfur content in sweet crude gave it a mildly sweet taste and a more pleasant smell. By contrast the high concentration of sulfur in sour crude caused it to smell similar to rotten eggs.
Why The Types of Crude Oil Matter
The factors used to classify crude oil matter throughout its lifecycle, from the initial recovery to the end refinement. The factors matter in the following ways:
Geographic Location - The crude oil’s geographic location will affect the drilling and recovery efforts in the upstream sector because the geology of the rock or shale will vary based on the region. One of the most important concerns regarding geographic locations, however, is transportation. Crude that is recovered far away from refineries and oil markets and without good access to pipelines will be much more expensive to transport than crude that is located within close proximity to a pipeline network.
API Gravity - The crude’s API gravity will impact its value as well as the quality of its yield. Light crude is more desirable than heavy crude because it produces a better yield and does not require as intensive refinement to produce a range of high value petroleum products.
Sulfur Content - Crude oil with a lower sulfur content, known as "sweet crude" is more desirable than high sulfur, or "sour crude" because the lower sulfur content means that the oil has less environmental impurities to remove and thus requires less refinement. The allowable sulfur content is also typically regulated and thus high sulfur crude requires a larger investment to meet acceptable levels.
The petroleum industry is continually innovating and advancing. New technology has allowed for the recovery of crude oil in geographic regions where it was once impossible. Likewise advances in the midstream phase of distribution are making transport safer, more efficient, and more reliable as refineries increase their capacity and capabilities. Crude oil and its various types will continue to be a staple of energy for the foreseeable future.
