Updated: April 13, 2026
The density of crude oil typically ranges from 800 to 1000 kg/m³ (20–70° API gravity). This single number determines how the oil is classified, priced, transported, and refined. Light crude fetches a premium because it yields more gasoline and diesel per barrel. Heavy crude costs less but demands more energy-intensive processing.
This guide covers crude oil density classification, the API gravity system, factors that affect density, and the measurement methods used in the field and in the lab.
Contents
- What Is the Density of Crude Oil?
- How Does API Gravity Relate to Crude Oil Density?
- How Is Crude Oil Classified by Density?
- What Factors Affect Crude Oil Density?
- How Do You Measure the Density of Crude Oil?
- Featured Density Meters for Crude Oil
- FAQ
What Is the Density of Crude Oil?
Crude oil density is the mass per unit volume, expressed in kg/m³ or g/cm³ at a reference temperature of 15°C (59°F). Most crude oils fall between 800 kg/m³ (light) and 1000 kg/m³ (extra-heavy). Anything above 1000 kg/m³ sinks in water.
In the oil industry, density is rarely stated in SI units. Instead, the API gravity scale is used. API gravity is inversely related to density — the lighter the oil, the higher the API number. This convention dates back to the American Petroleum Institute’s standardization efforts and remains the global norm for crude oil trading.
How Does API Gravity Relate to Crude Oil Density?
API gravity converts specific gravity (SG) into a more intuitive scale. The formula per ASTM D287 is:
API Gravity = (141.5 / SG at 60°F) − 131.5
Where SG is the ratio of the oil’s density to the density of water, both at 60°F (15.6°C). A crude oil with SG = 0.876 has an API gravity of 30°. Water has an API gravity of 10°.
| Crude Oil Type | Density (kg/m³) | Specific Gravity | API Gravity (°) |
|---|---|---|---|
| Extra Light | < 830 | < 0.830 | > 39 |
| Light | 830–870 | 0.830–0.870 | 31–39 |
| Medium | 870–920 | 0.870–0.920 | 22–31 |
| Heavy | 920–1000 | 0.920–1.000 | 10–22 |
| Extra Heavy / Bitumen | > 1000 | > 1.000 | < 10 |
How Is Crude Oil Classified by Density?
The industry classifies crude on two axes: density (API gravity) and sulfur content (sweet vs. sour). Both together determine pricing and refinery compatibility.
Light crude (API > 31°) flows easily, requires less refining energy, and yields a higher percentage of gasoline and diesel. West Texas Intermediate (WTI, ~39.6° API) and Brent (~38° API) are benchmark light crudes.
Medium crude (API 22–31°) balances yield and processing cost. Dubai/Oman crude falls in this range at ~31° API and serves as the pricing benchmark for Asian markets.
Heavy crude (API < 22°) is viscous, high in asphaltenes, and harder to transport. Canada’s oil sands produce heavy crude around 8–12° API. Moving this oil through pipelines requires diluent blending or heated lines. Refineries need coking or hydrocracking units to process it efficiently. For measuring flow rates in oil pipelines, accurate density data is essential for mass balance calculations.
What Factors Affect Crude Oil Density?
Four factors drive density variations between and within crude oil streams.
Temperature. Crude oil expands when heated. A typical coefficient of thermal expansion is 0.0008/°C. At 60°C, a crude oil that measures 870 kg/m³ at 15°C may read closer to 840 kg/m³. All density measurements must be corrected to the reference temperature (15°C per ASTM D1250 / API MPMS Chapter 11.1).
Composition. Light hydrocarbons (C5–C10) lower density. Heavy fractions — asphaltenes, resins, and polycyclic aromatics — increase it. Two crudes from the same field can differ by 20 kg/m³ depending on the production zone.
Sulfur content. Sulfur compounds are denser than most hydrocarbons. Sour crudes (sulfur > 0.5%) tend to be 10–30 kg/m³ denser than sweet crudes from similar geological formations.
Dissolved gas. Live crude (with dissolved gas at wellhead pressure) is lighter than dead crude (atmospheric, degassed). Custody transfer measurements always use stabilized (dead) crude to avoid gas interference.
How Do You Measure the Density of Crude Oil?
There are four main methods, each suited to different points in the production and supply chain.
Hydrometer (ASTM D1298)
A glass hydrometer floats in a sample cylinder. The scale reading at the meniscus gives density or API gravity directly. Simple, cheap, and widely used for spot checks and field sampling. Accuracy is typically ±0.5 kg/m³. The sample must be at a known temperature, and corrections are applied per ASTM D1250 tables.
Oscillating U-Tube (ASTM D4052)
A small glass U-tube is filled with the sample and vibrated electronically. The resonant frequency changes with the fluid’s density. Lab accuracy reaches ±0.0001 g/cm³. This is the reference method for lab-grade density measurement and is used for custody transfer disputes and quality certification per ISO 12185.
Coriolis Density Meter (Inline)
A Coriolis flow meter measures both mass flow rate and density simultaneously. The vibrating tubes’ resonant frequency shifts with fluid density. Accuracy is ±0.5 kg/m³ for density and ±0.1% for flow. This is the standard for custody transfer in pipelines and loading terminals. For details on Coriolis technology, see our flow rate and pressure relationship guide.
Tuning Fork Density Meter (Inline)
A vibrating tuning fork immersed in the process fluid changes frequency based on the surrounding fluid’s density. Accuracy is ±1 kg/m³. Compact, no moving parts, and works well for continuous monitoring in storage tanks and process lines. Particularly useful for heavy and viscous crude where other inline methods struggle with fouling.
| Method | Accuracy | Location | Standard | Best For |
|---|---|---|---|---|
| Hydrometer | ±0.5 kg/m³ | Field / Lab | ASTM D1298 | Spot checks, sampling |
| Oscillating U-Tube | ±0.1 kg/m³ | Lab | ASTM D4052 / ISO 12185 | Quality certification |
| Coriolis | ±0.5 kg/m³ | Inline | API MPMS Ch. 5.6 | Custody transfer |
| Tuning Fork | ±1.0 kg/m³ | Inline | — | Process monitoring |
Featured Density Meters for Crude Oil
Tuning Fork Density Meter
Accuracy: ±1 kg/m³ | Range: 0–3000 kg/m³ | 4–20 mA / HART
Coriolis Density Meter
Accuracy: ±0.5 kg/m³ | Dual measurement: flow + density
Handheld Digital Density Meter
Portable | ASTM D4052 | Lab and field sampling
FAQ
What is the density of crude oil in kg/m³?
Most crude oils range from 800 to 1000 kg/m³ at 15°C. Light crudes like WTI measure around 827 kg/m³. Heavy crudes from Venezuela or Canada can reach 1000 kg/m³ or higher. The exact value depends on composition, sulfur content, and dissolved gas.
What is the difference between API gravity and specific gravity?
Specific gravity is the ratio of oil density to water density (dimensionless, typically 0.80–1.00 for crude). API gravity is an inverted scale derived from SG: API = (141.5 / SG) − 131.5. Higher API means lighter oil. The two scales convey the same information in different formats.
Why does temperature matter for crude oil density measurement?
Crude oil expands approximately 0.08% per °C. A 40°C temperature difference can shift the density reading by 25–30 kg/m³. All official measurements are corrected to 15°C (60°F) using ASTM D1250 volume correction tables to ensure consistent comparisons. For pipeline operations, pressure transmitters work alongside density meters for accurate mass balance.
How do you measure crude oil density in a pipeline?
Coriolis meters are the standard for inline density measurement in pipelines. They measure mass flow and density simultaneously by detecting frequency shifts in vibrating tubes. Tuning fork density meters provide a simpler alternative for monitoring applications where custody-transfer accuracy is not required.
What is the density of diesel fuel compared to crude oil?
Diesel fuel density is 820–860 kg/m³ (API 33–41°). This falls in the same range as light crude oil. The key difference is that diesel is a refined product with a narrow composition range, while crude oil is a raw mixture with much wider density variation.
Can a Coriolis meter measure both flow and density of crude oil?
Yes. A Coriolis meter simultaneously measures mass flow rate (±0.1%), density (±0.5 kg/m³), and temperature. This makes it the preferred instrument for custody transfer metering where both volume and mass need to be reported.
Need a density meter for your crude oil application? Our process engineers can help you select the right instrument for your pipeline, storage tank, or lab. Contact us for a free technical consultation.
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