Viscosity of Crude Oil

Description and Classification Overview

Crude oil is a complex mixture of various components. Depending on its geographic origin, its chemical composition and consistency vary. The different types of crude oil need to be classified for further treatment. Both a crude oil's viscosity and its API (American Petroleum Institute) degree are important parameters for classification. Crude oil's viscosity can vary from a low-viscosity liquid to up to tar-like, nearly solid form.

Classification according to the API degree:

  • Light crude oil: API gravity higher than 31.1 °API (less than 870 kg/m³)
  • Medium crude oil: API gravity from 31.1 °API to 22.3 °API (870 to 920 kg/m³)
  • Heavy crude oil: API gravity from 22.3 °API to 10 °API (920 to 1000 kg/m³)
  • Extra-heavy crude oil: API gravity below 10 °API (higher than 1000 kg/m³)

The API degrees indicate whether a crude oil floats on water or sinks. Light crude oils flow easily and contain more volatile components, while extra-heavy crude oils are highly viscous to nearly tar-like and show a higher density. Intermediate oils are between these extremes.

According to the sulfur content, it can be distinguished between:

  • Sweet crude: sulfur content up to 1 % *
  • Sour crude: sulfur content higher than 1 %

*Different sources state a different maximum percentage of sulfur content for sweet crudes (between 0.42 % up to 1 %).

The tables below show examples for different crude oils and their typical values for kinematic viscosity and °API.

Viscosity Table – Measurement data

Crude oils - viscosity and °API

Typical values obtained from producer's data sheets.

Crude Oil Kin. Viscosity [mm²/s] at Temp. API Gravity °API
Arabian Light 10.7 at 20 °C 34.2
Brent 2.86 at 50 °C 37.9 ... 38.2
Bonny Light 2.90 at 50 °C 35.4 ... 35.8
Boscan 11233 at 100 °F 10.1
Escalante 307 at 38 °C 39.6
Kutubu 2.1 at 20 °C 44
Tia Juana Light 8.8 at 100 °F 31.9
Tia Juana Heavy 88.6 at 100 °F 12.3
West Texas Intermediate 4.9 at 20 °C 39


U.S. Energy Information Administration

Genesis Group, USA

Chevron Crude Oil Marketing

Exxon Mobil

AMSA-Australian Maritime Safety Authority


Reference U.S. Energy Information Administration, Genesis Group, USA, Chevron Crude Oil Marketing, Exxon Mobil, AMSA-Australian Maritime Safety Authority
Kin. vis. yes
Dyn. vis. no
Density yes
Multiple temperatures yes
Related Crude oil, heavy crude, sweet crude, sour crude, light crude oil, petroleum, viscosity, API gravity, °API