Remember these basics: "light" versus "heavy" refers to API gravity, "sweet" versus "sour" refers to sulfur content, WTI and Brent are geographic benchmarks that give us a glimpse of the prices buyers, sellers are circling around on the open market
A Crude Primer: Would a Barrel of Oil by Any Other Name Smell as Sweet?
When people talk about a barrel of crude oil, there is a tendency to lump all of it into one large category. The reality is that there are different flows of crude oil from all over the world that have various, distinct qualities. There are two main qualities used in the classification process. The first is API gravity and the second is the sulfur content.
API gravity is a measure of the density of oil on a "light to heavy" scale. Generally, "light crude" has an API gravity greater than 38° and "heavy crude" has an API gravity of less than 22°. Water by comparison has an API gravity of 10°. Some heavy crude is dense enough to sink in water.
The sulfur scale ranges from "sweet to sour". If oil has a sulfur content of less than 0.5 percent it is considered "sweet," and if it is above 0.5 percent it is considered "sour." Oil that is heavy or sour requires a more complex, more intensive, and more expensive refining process.
