Crude Oil Types: Light, Heavy, Sweet and Sour Guide

Economic Warfare & Trade Policy Energy & commodities

No two crude oils are exactly alike. A barrel pumped from a West Texas shale well, one loaded at a Mexican export terminal and one blended from Canadian oil sands differ in how dense they are, how much sulfur they carry and how much gasoline, diesel and jet fuel a refinery can pull out of them. Those differences decide where each crude can be processed and how much buyers will pay for it. This guide explains the two measurements the industry relies on, how the main crude categories compare, and what happens to a barrel once it reaches a refinery.

What crude oil is

The U.S. Energy Information Administration (EIA) defines crude oil as a mixture of hydrocarbons that is liquid in underground reservoirs and stays liquid at normal atmospheric pressure after it passes through surface separating equipment. Alongside the hydrocarbons, a crude stream can contain small amounts of non-hydrocarbons, including sulfur and various metals. Refineries turn it into heating oils, gasoline, diesel and jet fuel, lubricants, asphalt, propane and butane, and feedstocks for chemicals and plastics.

The EIA groups the properties that matter most to a refiner under the term “crude oil qualities”: sulfur content and API gravity. Together they affect how complex the processing has to be and what the finished products look like.

Measure one: API gravity (light vs. heavy)

API gravity is a scale created by the American Petroleum Institute to express the density of liquid petroleum. It is calculated from specific gravity measured at 60°F:

Degrees API = (141.5 ÷ specific gravity) − 131.5

The scale runs backward from what many people expect: the higher the API number, the lighter (less dense) the oil. Water works out to 10 degrees API on this formula, so oil above 10 degrees floats on water.

The cut-off points are not fixed by law, and the EIA itself uses two sets. Its petroleum data definitions describe light crude as generally above 38 degrees API, heavy crude as 22 degrees or below, and intermediate (often called medium) crude as the range between. A 2017 EIA analysis used a simpler split, calling crude below 25 degrees heavy and above 35 degrees light. Readers comparing reports should check which definition a source is using.

Measure two: sulfur (sweet vs. sour)

Sulfur content is measured as a percentage of weight. The EIA defines crude with less than 1% sulfur as sweet and crude with more than 1% as sour. Individual contracts can be much stricter. The New York Mercantile Exchange (NYMEX) light sweet crude oil futures contract, the main trading contract for West Texas Intermediate (WTI), requires domestic deliveries to have 0.42% sulfur or less and an API gravity between 37 and 42 degrees, with delivery at Cushing, Oklahoma.

Sulfur matters because finished fuels must meet low-sulfur specifications. According to the EIA, sour crude needs more complex refinery processing to meet those specifications and to avoid damaging refinery equipment.

The four main combinations

Putting the two measures together gives the categories traders use every day.

Light sweet. Low density and low sulfur. Much of the growth in U.S. production has come from shale formations in the Lower 48 states, which the EIA says contain primarily light crude. WTI and Louisiana Light Sweet (LLS) are U.S. examples, and the EIA has pointed to Libya and Nigeria as producers of light sweet grades.
Light or medium sour. Similar density to light sweet but more sulfur, so refiners must add desulfurization before the fuels can be sold.
Heavy sweet. Dense but relatively low in sulfur.
Heavy sour. Dense and high in sulfur. The EIA cites Mexico’s Maya and Western Canada Select (WCS) as heavy grades commonly bought by U.S. refiners.

Why light sweet crude usually costs more

The EIA says light, sweet crude oils are usually priced higher than heavy, sour crude oils. The reason is the product mix. Gasoline and diesel normally sell at a large premium to residual fuel oil and other “bottom of the barrel” products, and light sweet crude can produce them more easily and more cheaply, using less sophisticated and less energy-intensive refineries.

The gap between grades moves with supply. In 2017, as OPEC production cuts and declines in Canada, Mexico and Venezuela reduced the supply of medium and heavy crude while light crude output grew, the EIA reported that the premium for LLS over Maya on the U.S. Gulf Coast narrowed from $9 a barrel in March to $5 in August. Over the same months, WTI’s premium over WCS in the Midwest narrowed from $13 to $10 a barrel. Those figures are a historical example, not current prices.

What a refinery does with a barrel

A U.S. barrel holds 42 gallons. Refining starts with atmospheric distillation, which heats crude to roughly 600°F to 750°F, depending on the crude and the products wanted, and separates it into fractions as the vapors cool and condense. Light gases and naphtha come off the top, jet fuel and diesel-range oils in the middle, and heavy residue at the bottom.

What happens next depends on how complex the refinery is:

Catalytic cracking breaks large, heavy molecules into lighter ones and, the EIA notes, is an effective way to raise gasoline yield.
Hydrocracking uses hydrogen and catalysts at high pressure to turn heavier material into gasoline components, jet fuel and other products, and can handle high-sulfur feeds.
Coking thermally cracks the heaviest residue into lighter oils, leaving petroleum coke as a by-product.
Hydrotreating uses hydrogen to remove sulfur and nitrogen compounds from fuel streams.
Catalytic reforming rearranges molecules in low-octane naphtha to make higher-octane gasoline blending stock and petrochemical feedstocks.

The EIA says processing heavy sour crude requires these extra units, specifically crackers, cokers and hydrotreaters, to get light products out of it. When a refinery uses simple distillation alone on heavier crude, it ends up with more low-value products.

What comes out: the average U.S. barrel

From each 42-gallon barrel of crude, U.S. refineries on average produce, according to the EIA:

About 19 to 20 gallons of motor gasoline
11 to 13 gallons of distillate fuel, most of it sold as diesel
3 to 5 gallons of jet fuel

More than a dozen other products make up the rest, including liquids used by the petrochemical industry. The exact mix shifts month to month as refiners respond to demand and margins.

Why refinery location matters

Because moving oil costs money, refiners often build their equipment around the crude that is easiest to reach. The EIA notes that U.S. Gulf Coast refineries are typically supplied with heavy Mexican and South American crude and are more complex than East Coast refineries, which run lighter, sweeter crude from the Atlantic Basin. Complex plants pay more to build but gain flexibility: they can buy cheaper heavy sour grades when the price gap is wide. When that gap narrows, as it did in 2017, their advantage shrinks.

Why it matters to drivers and markets

Crude quality helps explain headlines that otherwise seem puzzling: why one benchmark trades several dollars away from another, why a supply disruption in one heavy-oil producer can hit some refineries harder than others. For background on how oil prices feed into the wider economy, see our Economics Hub. For coverage of shipping risks in the Strait of Hormuz, see our explainer on war-risk insurance rates.

Additional details

The NYMEX WTI contract also limits viscosity, pour point, water and sediment, carbon residue, acidity and metals such as nickel and vanadium.
The EIA’s light/heavy chart of world crudes notes that it is a selection of grades, not a complete list, and that some crudes fall outside the range it shows.
This guide was first published March 12, 2026, and was rewritten and expanded Oct. 21, 2026, with new sourcing.

Sources

U.S. EIA, Crude oil quality: definitions and explanatory notes (API gravity formula, light/intermediate/heavy ranges, crude oil definition)
U.S. EIA, “Changing quality mix is affecting crude oil price differentials and refining decisions” (Sept. 21, 2017)
U.S. EIA, “Crude oils have different quality characteristics” (July 16, 2012)
U.S. EIA, Refining crude oil (Energy Explained)
U.S. EIA, Refining crude oil: inputs and outputs
U.S. EIA, Refinery capacity: definitions (distillation, cracking, hydrotreating, reforming)
CME Group, NYMEX Rulebook Chapter 200: Light Sweet Crude Oil Futures

Photo: Refinery at Anacortes, Washington, by Walter Siegmund, CC BY 2.5, via Wikimedia Commons.

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Crude Oil Types Explained: API Gravity, Sulfur and What Refineries Make