In the oil industry, API stands for the American Petroleum Institute, the trade association that developed the gravity scale used to measure how heavy or light a crude oil is. When you see “API gravity” on an energy report or oil price listing, it refers to a specific measurement, expressed in degrees, that tells refiners and traders how dense a particular crude oil is compared to water.
How API Gravity Works
API gravity is an inverted scale. The higher the number, the lighter and less dense the oil. The lower the number, the heavier and thicker it is. Water itself sits at exactly 10 degrees API. Any crude oil with an API gravity above 10 is lighter than water and will float on it, while anything below 10 is heavier than water and will sink.
The measurement is calculated using a formula that compares the oil’s specific gravity (its density relative to water at 60°F) to a fixed reference point. In practical terms, you don’t need to run the math yourself. What matters is understanding the scale: a crude oil at 45 degrees API is thin and flows easily, while one at 15 degrees API is thick, almost tar-like, and much harder to process.
What the Degree Ranges Mean
The U.S. Energy Information Administration breaks crude oil into three broad categories based on API gravity:
- Light crude: Above 38 degrees API. This oil flows freely, is easier to refine, and yields a higher percentage of gasoline and diesel.
- Intermediate (medium) crude: Between 22 and 38 degrees API. This is the middle ground, requiring more processing than light crude but still commercially attractive.
- Heavy crude: 22 degrees API or below. This thick oil needs more energy, more complex refinery equipment, and more processing steps to turn into usable fuel.
Some industry sources add a fourth category, extra-heavy crude, for anything below roughly 10 degrees API. These oils are so dense they barely flow at room temperature and sometimes need to be diluted or heated just to move through a pipeline.
Why API Gravity Affects Oil Prices
Lighter crudes are generally worth more per barrel because they produce a larger share of high-value products like gasoline, jet fuel, and diesel with less refining effort. Heavy crudes cost less per barrel but require specialized refineries equipped with coking units or other heavy processing equipment.
EIA pricing data from January 2026 illustrates the gap clearly. Domestic crude with an API gravity of 20 degrees or less sold for about $64.25 per barrel, while crude in the 25.1 to 30.0 degree range fetched $55.74. That may seem counterintuitive (heavier oil costing more), but pricing also reflects sulfur content, regional supply constraints, and the specific refineries buying each grade. In global markets, the general pattern holds: light, low-sulfur crudes like Brent and West Texas Intermediate command premium prices because they are cheaper and simpler to refine.
Where You’ll See API Gravity Referenced
If you’re reading about oil markets, energy policy, or petroleum engineering, API gravity shows up constantly. Benchmark crudes are often described by their API gravity alongside their sulfur content. West Texas Intermediate, for example, typically falls around 39 to 40 degrees API, making it a light crude. Heavier benchmarks from other regions can sit in the low 20s or even the teens.
Refineries are built to handle specific API gravity ranges. A refinery designed for light crude can’t simply switch to processing heavy crude without costly upgrades, and vice versa. This is one reason oil markets don’t treat all barrels as interchangeable. When you hear that a country’s oil production is “heavy sour” or “light sweet,” the first word refers to API gravity (heavy or light) and the second to sulfur content (sour means high sulfur, sweet means low).
The Organization Behind the Name
The American Petroleum Institute itself is a Washington, D.C.-based trade group representing oil and natural gas companies. Founded in 1919, it develops technical standards used across the industry, from pipeline specifications to equipment certifications. The API gravity scale is just one of hundreds of standards the organization maintains, but it’s by far the most widely recognized outside the industry. When someone mentions “API” in the context of oil, they’re almost always talking about the gravity measurement rather than the organization itself.